Method for determining resource for transmitting signal in wireless communications system and apparatus therefor

ABSTRACT

There is provided a method for performing device-to-device (D2D) communication in a wireless communication system, the method comprising: by a first device, acquiring a resource pool for the D2D communication, wherein the resource pool includes a SA (scheduling assignment) resource pool indicating a resource region for SA transmission and a data resource pool indicating a resource region for D2D data transmission; performing D2D synchronization with a base station or a specific device; transmitting a SA (scheduling assignment) to a second device using the SA resource pool.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2015/003826, filed on Apr. 16, 2015,which claims the benefit of U.S. Provisional Application No. 61/981,167,filed on Apr. 17, 2014, the contents of which are all herebyincorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, and,more particularly, to a method and device for determining a resource forsignal transmission in a wireless communication system supportingdevice-to-device communication (D2D communication).

BACKGROUND ART

A mobile communication system has been developed to provide users withmobility and voice services. Further, the mobile communication systemhas provided the user with data services. Thus, currently, due anexplosive traffic increase, resources are deficient. Further, the usersdemand faster communication services. Thus, there is a need for animproved mobile communication system.

A future mobile communication system should deal with the explosive datatraffic, provide an increased transmission amount per a user, accept alarger number of connected devices, provide a very low end-to-endlatency, and a high energy efficiency. To this end, dual connectivity,massive multiple input multiple output, in-band full duplex, NOMA(Non-Orthogonal Multiple Access), super wideband support, devicenetworking, etc. have been studied.

DISCLOSURE Technical Problem

The present disclosure is to provide a method for determining a resourcefor D2D communication.

Further, the present disclosure is to provide a method for transmittinga SA (scheduling assignment) to prevent collisions between SAtransmissions for D2D communication.

Further, the present disclosure is to provide a method for performing SAinitial transmission using a random backoff scheme.

Further, the present disclosure is to provide a method for performing SAre-transmission using a probabilistic scheme.

Further, the present disclosure is to provide a method for informingwhether to perform further SA transmission using a SA confirmation flag.

The objectives of the present disclosure are limited to the above.Further objectives thereof may be apparent from the skilled person tothe art from reading a following description.

Technical Solution

In one aspect of the present disclosure, there is provided a method forperforming device-to-device (D2D) communication in a wirelesscommunication system, the method comprising: by a first device,acquiring a resource pool for the D2D communication, wherein theresource pool includes a SA (scheduling assignment) resource poolindicating a resource region for SA transmission and a data resourcepool indicating a resource region for D2D data transmission; performingD2D synchronization with a base station or a specific device; sending(or transmitting) a SA (scheduling assignment) to a second device usingthe SA resource pool, wherein the SA includes information related to D2Ddata transmission; and sending D2D data to the second device, whereinthe SA resource pool includes at least one of first and second SAresource pools, wherein in the first pool, a SA resource is determinedin a non-contention manner, and, in the second pool, a SA resource isdetermined in a contention manner, wherein the second SA resource poolincludes one or more contention windows (CWs).

In one embodiment, the first device sending the SA (schedulingassignment) to the second device comprises the first device sendingmultiple SAs in the second SA resource pool to the second device.

In one embodiment, the first device sending the multiple SAs in thesecond SA resource pool to the second device comprises: the first deviceperforming SA initial transmission in a first CW in the second SAresource pool; and the first device performing SA re-transmission in asecond CW following the first CW.

In one embodiment, the first device performing the SA initialtransmission comprises: the first device determining a random backoffvalue corresponding to a CW for the SA initial transmission; and thefirst device performing the SA initial transmission in the CWcorresponding to the determined random backoff value.

In one embodiment, the random backoff values are determined with thesame probability for all CWs in the second SA resource pool; or therandom backoff values are determined such that probabilities thereof arebased on precedence of corresponding CWs.

In one embodiment, the first device performing the SA re-transmissioncomprising: the first device computing a probability value for the SAre-transmission in the second CW; and the first device performing the SAre-transmission in the second CW based on the computed probabilityvalue.

In one embodiment, the probability value is determined as a valueminimizing a sum of a probability that all devices perform SAre-transmission in the second CW and a probability that any device doesnot perform SA re-transmission in the second CW.

In one embodiment, the probability value is determined withconsideration of a number of devices undergoing collisions for SAtransmission and/or a number of remaining CWs.

In one embodiment, the SA initial transmission and re-transmission areconducted based on an SA resource interference measured in previous CWsto a current CW for the SA transmission and/or the first SA resourcepool information.

In one embodiment, the first device performing the SA initialtransmission comprises: comparing a receiving energy value for the firstCW with a predetermined first threshold value or second threshold value;and determining whether to perform the SA initial transmission based onthe comparison, wherein the first threshold value is an energy levelcorresponding to an empty resource and the second threshold value is amaximum interference level at which the SA transmission is acceptable.

In one embodiment, when the receiving energy value is smaller than thepredetermined first threshold value, the first device performs the SAinitial transmission using the SA resource in the first CW.

In one embodiment, when the receiving energy value is larger than thepredetermined second threshold value, the first device gives upperforming the SA initial transmission in the first CW.

In one embodiment, the SA (scheduling assignment) sent to the seconddevice further includes a SA confirmation flag field to indicate whethera further SA transmission is present after the SA transmission.

In one embodiment, the specific device includes a cluster header (CH)device or representative device in a D2D device group or a device at acoverage border.

In another aspect of the present disclosure, there is provided a devicefor performing device-to-device (D2D) communication in a wirelesscommunication system, the device comprising: a RF (radio frequency) unitconfigured to receive or send a RF signal; and a processor functionallycoupled to the RF unit, wherein the processor is configured: to acquirea resource pool for the D2D communication, wherein the resource poolincludes a SA (scheduling assignment) resource pool indicating aresource region for SA transmission and a data resource pool indicatinga resource region for D2D data transmission; to perform D2Dsynchronization with a base station or a specific device; to send a SA(scheduling assignment) to another device using the SA resource pool,wherein the SA includes information related to D2D data transmission;and to send D2D data to said another device, wherein the SA resourcepool includes at least one of first and second SA resource pools,wherein in the first pool, a SA resource is determined in anon-contention manner, and, in the second pool, a SA resource isdetermined in a contention manner, wherein the second SA resource poolincludes one or more contention windows (CWs).

Advantageous Effects

In accordance with the present disclosure, the SA initial transmissionusing the random backoff scheme may reduce the collisions between the SAtransmissions.

Further, in accordance with the present disclosure, the multiple SAstransmission, that is, the SA re-transmission using the probabilisticscheme may allow the receiving device to receive the SA correctly inspite of the collision occurrence between the SA transmissions, therebylead to accurate D2D communication.

Further, in accordance with the present disclosure, whether to performthe further SA transmission may be correctly informed to the receivingdevice, by performing the SA transmission with the SA confirmation flagcontained therein, thereby to remove an unnecessary monitoring to savethe power consumption.

The effects of the present disclosure are limited to the above. Furthereffects thereof may be apparent from the skilled person to the art fromreading a following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification and in which like numerals depict like elements,illustrate embodiments of the present disclosure and, together with thedescription, serve to explain the principles of the disclosure.

FIG. 1 illustrates a structure of a radio frame in a wirelesscommunication system where the present invention is applicable.

FIG. 2 illustrates a resource grid for one downlink slot in a wirelesscommunication system where the present invention is applicable.

FIG. 3 illustrates a structure of a downlink sub-frame in a wirelesscommunication system where the present invention is applicable.

FIG. 4 illustrates a structure of an uplink sub-frame in a wirelesscommunication system where the present invention is applicable.

FIG. 5 illustrates one example of a mapping of PUCCH formats with aPUCCH region of an uplink physical resource block in a wirelesscommunication system where the present invention is applicable.

FIG. 6 illustrates a structure of a CQI channel for a general CP in awireless communication system where the present invention is applicable.

FIG. 7 illustrates a structure of an ACK/NACK channel for a general CPin a wireless communication system where the present invention isapplicable.

FIG. 8 illustrates one example of generating and sending 5 SC-FDMAsymbols for one slot in a wireless communication system where thepresent invention is applicable.

FIG. 9 illustrates one example of merging between component carriers ina wireless communication system where the present invention isapplicable.

FIG. 10 illustrates one example of a sub-frame structure based oncross-carrier scheduling in a wireless communication system where thepresent invention is applicable.

FIG. 11 illustrates one example of transmission channel processing ofUL-SCH in a wireless communication system where the present invention isapplicable.

FIG. 12 illustrates one example of signal processing and definition ofan uplink shared channel as a transport channel in a wirelesscommunication system where the present invention is applicable.

FIG. 13 illustrates a configuration of a conventional MIMO antennacommunication system.

FIG. 14 illustrates a channel from multiple sending antennas to onereceiving antenna.

FIG. 15 illustrates a reference signal pattern mapped with a downlinkresource block pair in a wireless communication system where the presentinvention is applicable.

FIG. 16 illustrates an uplink sub-frame including a sounding referencesignal symbol in a wireless communication system where the presentinvention is applicable.

FIG. 17 illustrates relay node resource division in a wirelesscommunication system where the present invention is applicable.

FIG. 18 conceptionally illustrates D2D communication in a wirelesscommunication system where the present invention is applicable.

FIG. 19 illustrates one example among various scenarios for D2Dcommunication where a method as disclosed herein is applicable.

FIG. 20 illustrates one example of discovery resource assignment inaccordance with one embodiment of the present invention.

FIG. 21 schematically illustrate discovery process in accordance withone embodiment of the present invention.

FIG. 22 illustrates one example of a D2D resource pool configurationwhere methods as disclosed herein are applicable.

FIG. 23 illustrates one example of a D2D resource pool configurationwhere methods as disclosed herein are applicable.

FIG. 24 is a schematic view of one example of a wireless communicationsystem where methods as disclosed herein are applicable.

FIG. 25 illustrates one example of a SA resource pool where methods asdisclosed herein are applicable, and a SA transmission method.

FIG. 26 is a graph illustrating one example of SA re-transmissionprobability values in a specific CW for a SA re-transmission methodusing the probabilistic scheme as disclosed herein.

FIG. 27 illustrates one example of a SA re-transmission method asdisclosed herein.

FIG. 28 to FIG. 30 illustrate examples of flow-charts of a SAtransmission and SA re-transmission method as disclosed herein.

FIG. 31 illustrates a block diagram of a wireless communication devicewhere methods as disclosed herein are applicable.

MODE FOR INVENTION

Hereafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Adetailed description to be disclosed hereinbelow together with theaccompanying drawing is to describe embodiments of the present inventionand not to describe a unique embodiment for carrying out the presentinvention. The detailed description below includes details in order toprovide a complete understanding. However, those skilled in the art knowthat the present invention can be carried out without the details.

In some cases, in order to prevent a concept of the present inventionfrom being ambiguous, known structures and devices may be omitted or maybe illustrated in a block diagram format based on core function of eachstructure and device.

In the specification, a base station means a terminal node of a networkdirectly performing communication with a terminal. In the presentdocument, specific operations described to be performed by the basestation may be performed by an upper node of the base station in somecases. That is, it is apparent that in the network constituted bymultiple network nodes including the base station, various operationsperformed for communication with the terminal may be performed by thebase station or other network nodes other than the base station. A basestation (BS) may be generally substituted with terms such as a fixedstation, Node B, evolved-NodeB (eNB), a base transceiver system (BTS),an access point (AP), and the like. Further, a ‘terminal’ may be fixedor movable and be substituted with terms such as user equipment (UE), amobile station (MS), a user terminal (UT), a mobile subscriber station(MSS), a subscriber station (SS), an advanced mobile station (AMS), awireless terminal (WT), a Machine-Type Communication (MTC) device, aMachine-to-Machine (M2M) device, a Device-to-Device (D2D) device, andthe like.

Hereinafter, a downlink means communication from the base station to theterminal and an uplink means communication from the terminal to the basestation. In the downlink, a transmitter may be a part of the basestation and a receiver may be a part of the terminal. In the uplink, thetransmitter may be a part of the terminal and the receiver may be a partof the base station.

Specific terms used in the following description are provided to helpappreciating the present invention and the use of the specific terms maybe modified into other forms within the scope without departing from thetechnical spirit of the present invention.

The following technology may be used in various wireless access systems,such as code division multiple access (CDMA), frequency divisionmultiple access (FDMA), time division multiple access (TDMA), orthogonalfrequency division multiple access (OFDMA), single carrier-FDMA(SC-FDMA), non-orthogonal multiple access (NOMA), and the like. The CDMAmay be implemented by radio technology universal terrestrial radioaccess (UTRA) or CDMA2000. The TDMA may be implemented by radiotechnology such as Global System for Mobile communications (GSM)/GeneralPacket Radio Service (GPRS)/Enhanced Data Rates for GSM Evolution(EDGE). The OFDMA may be implemented as radio technology such as IEEE802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, E-UTRA (Evolved UTRA),and the like. The UTRA is a part of a universal mobile telecommunicationsystem (UMTS). 3rd generation partnership project (3GPP) long termevolution (LTE) as a part of an evolved UMTS (E-UMTS) using evolved-UMTSterrestrial radio access (E-UTRA) adopts the OFDMA in a downlink and theSC-FDMA in an uplink. LTE-advanced (A) is an evolution of the 3GPP LTE.

The embodiments of the present invention may be based on standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2 whichare the wireless access systems. That is, steps or parts which are notdescribed to definitely show the technical spirit of the presentinvention among the embodiments of the present invention may be based onthe documents. Further, all terms disclosed in the document may bedescribed by the standard document.

3GPP LTE/LTE-A is primarily described for clear description, buttechnical features of the present invention are not limited thereto.

General System

FIG. 1 illustrates a structure a radio frame in a wireless communicationsystem to which the present invention can be applied.

In 3GPP LTE/LTE-A, radio frame structure type 1 may be applied tofrequency division duplex (FDD) and radio frame structure type 2 may beapplied to time division duplex (TDD) are supported.

FIG. 1(a) exemplifies radio frame structure type 1. The radio frame isconstituted by 10 subframes. One subframe is constituted by 2 slots in atime domain. A time required to transmit one subframe is referred to asa transmissions time interval (TTI). For example, the length of onesubframe may be 1 ms and the length of one slot may be 0.5 ms.

One slot includes a plurality of orthogonal frequency divisionmultiplexing (OFDM) symbols in the time domain and includes multipleresource blocks (RBs) in a frequency domain. In 3GPP LTE, since OFDMA isused in downlink, the OFDM symbol is used to express one symbol period.The OFDM symbol may be one SC-FDMA symbol or symbol period. The resourceblock is a resource allocation wise and includes a plurality ofconsecutive subcarriers in one slot.

FIG. 1(b) illustrates frame structure type 2. Radio frame type 2 isconstituted by 2 half frames, each half frame is constituted by 5subframes, a downlink pilot time slot (DwPTS), a guard period (GP), andan uplink pilot time slot (UpPTS), and one subframe among them isconstituted by 2 slots. The DwPTS is used for initial cell discovery,synchronization, or channel estimation in a terminal. The UpPTS is usedfor channel estimation in a base station and to match uplinktransmission synchronization of the terminal. The guard period is aperiod for removing interference which occurs in uplink due tomulti-path delay of a downlink signal between the uplink and thedownlink.

In frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether the uplink and the downlinkare allocated (alternatively, reserved) with respect to all subframes.Table 1 shows the uplink-downlink configuration.

TABLE 1 Uplink- Downlink- Downlink to-Uplink config- Switch-pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U UD S U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D DD D D 6 5 ms D S U U U D S U U D

Referring to Table 1, for each sub frame of the radio frame, ‘D’represents a subframe for downlink transmission, ‘U’ represents asubframe for uplink transmission, and ‘S’ represents a special subframeconstituted by three fields such as the DwPTS, the GP, and the UpPTS.The uplink-downlink configuration may be divided into 7 configurationsand the positions and/or the numbers of the downlink subframe, thespecial subframe, and the uplink subframe may vary for eachconfiguration.

A time when the downlink is switched to the uplink or a time when theuplink is switched to the downlink is referred to as a switching point.Switch-point periodicity means a period in which an aspect of the uplinksubframe and the downlink subframe are switched is similarly repeatedand both 5 ms or 10 ms are supported. When the period of thedownlink-uplink switching point is 5 ms, the special subframe S ispresent for each half-frame and when the period of the downlink-uplinkswitching point is 5 ms, the special subframe S is present only in afirst half-frame.

In all configurations, subframes #0 and #5 and the DwPTS are intervalsonly the downlink transmission. The UpPTS and a subframe justsubsequently to the subframe are continuously intervals for the uplinktransmission.

The uplink-downlink configuration may be known by both the base stationand the terminal as system information. The base station transmits onlyan index of configuration information whenever the uplink-downlinkconfiguration information is changed to announce a change of anuplink-downlink allocation state of the radio frame to the terminal.Further, the configuration information as a kind of downlink controlinformation may be transmitted through a physical downlink controlchannel (PDCCH) similarly to other scheduling information and may becommonly transmitted to all terminals in a cell through a broadcastchannel as broadcasting information.

The structure of the radio frame is just one example and the numbersubcarriers included in the radio frame or the number of slots includedin the subframe and the number of OFDM symbols included in the slot maybe variously changed.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin the wireless communication system to which the present invention canbe applied.

Referring to FIG. 2, one downlink slot includes the plurality of OFDMsymbols in the time domain. Herein, it is exemplarily described that onedownlink slot includes 7 OFDM symbols and one resource block includes 12subcarriers in the frequency domain, but the present invention is notlimited thereto.

Each element on the resource grid is referred to as a resource elementand one resource block includes 12×7 resource elements. The number ofresource blocks included in the downlink slot, NDL is subordinated to adownlink transmission bandwidth.

A structure of the uplink slot may be the same as that of the downlinkslot.

FIG. 3 illustrates a structure of a downlink subframe in the wirelesscommunication system to which the present invention can be applied.

Referring to FIG. 3, a maximum of three fore OFDM symbols in the firstslot of the sub frame is a control region to which control channels areallocated and residual OFDM symbols is a data region to which a physicaldownlink shared channel (PDSCH) is allocated. Examples of the downlinkcontrol channel used in the 3GPP LTE include a Physical Control FormatIndicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH),a Physical Hybrid-ARQ Indicator Channel (PHICH), and the like.

The PFCICH is transmitted in the first OFDM symbol of the subframe andtransports information on the number (that is, the size of the controlregion) of OFDM symbols used for transmitting the control channels inthe subframe. The PHICH which is a response channel to the uplinktransports an Acknowledgement (ACK)/Not-Acknowledgement (NACK) signalfor a hybrid automatic repeat request (HARQ). Control informationtransmitted through a PDCCH is referred to as downlink controlinformation (DCI). The downlink control information includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for apredetermined terminal group.

The PDCCH may transport A resource allocation and transmission format(also referred to as a downlink grant) of a downlink shared channel(DL-SCH), resource allocation information (also referred to as an uplinkgrant) of an uplink shared channel (UL-SCH), paging information in apaging channel (PCH), system information in the DL-SCH, resourceallocation for an upper-layer control message such as a random accessresponse transmitted in the PDSCH, an aggregate of transmission powercontrol commands for individual terminals in the predetermined terminalgroup, a voice over IP (VoIP). A plurality of PDCCHs may be transmittedin the control region and the terminal may monitor the plurality ofPDCCHs. The PDCCH is constituted by one or an aggregate of a pluralityof continuous control channel elements (CCEs). The CCE is a logicalallocation wise used to provide a coding rate depending on a state of aradio channel to the PDCCH. The CCEs correspond to a plurality ofresource element groups. A format of the PDCCH and a bit number ofusable PDCCH are determined according to an association between thenumber of CCEs and the coding rate provided by the CCEs.

The base station determines the PDCCH format according to the DCI to betransmitted and attaches the control information to a cyclic redundancycheck (CRC) to the control information. The CRC is masked with a uniqueidentifier (referred to as a radio network temporary identifier (RNTI))according to an owner or a purpose of the PDCCH. In the case of a PDCCHfor a specific terminal, the unique identifier of the terminal, forexample, a cell-RNTI (C-RNTI) may be masked with the CRC. Alternatively,in the case of a PDCCH for the paging message, a paging indicationidentifier, for example, the CRC may be masked with a paging-RNTI(P-RNTI). In the case of a PDCCH for the system information, in moredetail, a system information block (SIB), the CRC may be masked with asystem information identifier, that is, a system information (SI)-RNTI.The CRC may be masked with a random access (RA)-RNTI in order toindicate the random access response which is a response to transmissionof a random access preamble.

Hereinafter, PDCCH will be described in details.

Control indicator to be transmitted over PDCCH is referred to as DCI(Downlink Control Indicator). As for the PDCCH, a size and usage of thecontrol indicator may vary based on a DCI format, and the size thereofmay considerably vary based on a coding rate.

A following table 2 shows DCI based on a DCI format:

TABLE 2 DCI format Objectives 0 Scheduling of PUSCH 1 Scheduling of onePDSCH codeword 1A Compact scheduling of one PDSCH codeword 1BClosed-loop single-rank transmission 1C Paging, RACH response anddynamic BCCH 1D MU-MIMO 2 Scheduling of rank-adapted closed-loop spatialmultiplexing mode 2A Scheduling of rank-adapted open-loop spatialmultiplexing mode 3 TPC commands for PUCCH and PUSCH with 2 bit poweradjustments 3A TPC commands for PUCCH and PUSCH with single bit poweradjustments 4 the scheduling of PUSCH in one UL cell with multi-antennaport transmission mode

Referring to the table 2, the DCI format may include a format 0 forscheduling of the PUSCH, a format 1 for scheduling of one PDSCHcodeword, a format 1A for compact-scheduling of one PDSCH codeword, aformat 1C for very compact-scheduling of DL-SCH, a format 2 forscheduling of the PDSCH in a closed-loop spatial multiplexing mode, aformat 2A for scheduling of the PDSCH in an open-loop spatialmultiplexing mode, formats 3 and 3A for transmission of TPC(Transmission Power Control) commands for an uplink channel, and aformat 4 for scheduling of the PUSCH in one uplink cell in amulti-antenna port transmission mode.

DCI format 1A may be used for the PDSCH scheduling regardless of whichtransmission mode is set in a device.

The DCI format may be individually applied between devices, and PDCCHsof multiple devices may be multiplexed in one subframe. The PDCCH may beformed of one CCE (control channel elements) or an aggregation ofseveral continuous CCEs. The CCE may refer to a logical assignment unitused to provide the PDCCH with a coding rate based on a state of awireless channel. The CCE may refer to a unit corresponding to nine setsof REGs formed of four resource elements. A base station may use {1, 2,4, 8} CCEs for configuring one PDCCH signal, where {1, 2, 4, 8} may bereferred to as a CCE aggregation level.

A number of CCEs used for transmission of a specific PDCCH may bedetermined by the base station based on a channel state. The PDCCHconfigured for each device may be interleaved and mapped into a controlchannel region of each subframe based on a CCE-to-RE mapping rule. Alocation of the PDCCH may vary depending on a number of OFDM symbols fora control channel of each subframe, a number of PHICH groups, andtransmission antennas and frequency transitions, etc.

As described above, a multiplexed PDCCH of each device may beindividually subjected to channel coding, and CRC (Cyclic RedundancyCheck). A unique ID (UE ID) of each device may be masked to the CRC toallow the device to receive its PDCCH. However, over control regionallocated in the subframe, the base station may not provide anyinformation about where the PDCCH corresponding to the device is. Sincethe device is not aware of where its PDCCH is, what CCE aggregationlevel is, or which DCI format is used for transmission for receiving thecontrol channel transmitted from the base station, the device may findits PDCCH by monitoring PDCCH candidates in the subframe. This may bereferred to BD (Blind Decoding).

The blind decoding may be referred to blind detection or blind search.The blind decoding may refer to the device de-masking its deviceidentifier (UE ID) to the CRC and, thereafter, checking the CRC error todetermine whether that PDCCH is its control channel.

Hereinafter, information transmitted via the DCI format 0 will bedescribed.

The DCI format 0 may be used for scheduling of PUSCH in one uplink cell.

A following table 3 shows information transmitted via the DCI format 0:

TABLE 3 Format 0 (Release 8) Format 0 (Release 10) Carrier Indicator(CIF) Flag for format 0/format 1A Flag for format 0/format 1Adifferentiation differentiation Hopping flag (FH) Hopping flag (FH)Resource block assignment (RIV) Resource block assignment (RIV) MCS andRV MCS and RV NDI (New Data Indicator) NDI (New Data Indicator) TPC forPUSCH TPC for PUSCH Cyclic shift for DM RS Cyclic shift for DM RS ULindex (TDD only) UL index (TDD only) Downlink Assignment Index (DAI)Downlink Assignment Index (DAI) CSI request (1 bit) CSI request (1 or 2bits: 2 bit is for multi carrier) SRS request Resource assignment type(RAT)

Referring to the table 3, the information transmitted via the DCI format0 are as follows:

1) A carrier indicator—this may be formed of 0 or 3 bits.

2) A flag to distinguish between the DCI format 0 and format 1A—this maybe formed of 1 bit, where 0 value indicates the DCI format 0 and 1 valueindicates the DCI format 1A.

3) A frequency hopping flag—this may be formed of 1 bit. This field maybe used for multi-cluster assignment of MSB (Most Significant bit) of anassociated resource assignment if necessary.

4) Resource block assignment and hopping resource assignment—this may beformed of ┌log₂(N_(RB) ^(DL)(N_(RB) ^(DL)+1)/2┐ bits. In thisconnection, with the PUSCH hopping in a single-cluster assignment, inorder to obtain a ñ_(PRB)(i) value, NUL_hop MSBs may be used.(┌log₂(N_(RB) ^(UL)(N_(RB) ^(UL)+1)/2)┐−N_(UL) _(_) _(hop)) bits mayprovide resource assignment of a first slot in an uplink subframe.Further, without the PUSCH hopping in the single cluster assignment,(┌log₂(N_(RB) ^(UL)(N_(RB) ^(UL)+1)/2)┐ bits may provide resourceassignment in the uplink subframe. Further, without the PUSCH hopping inmulti-cluster assignment, resource assignment information may beacquired from concatenation of a frequency hopping flag field andresource block assignment and a hopping resource assignment field, and

$\left\lceil {\log_{2}\left( \begin{pmatrix}\left\lceil {{N_{RB}^{UL}/P} + 1} \right\rceil \\4\end{pmatrix} \right)} \right\rceil$bits may provide the resource assignment in the uplink subframe. In thisconnection, a P value may be determined by a number of downlink resourceblocks.

5) MCS (Modulation and coding scheme)—this may be formed of 5 bits.

6) New data indicator—this may be formed of 1 bit.

7) TPC (Transmit Power Control) command for PUSCH—this may be formed of2 bits.

8) CS (cyclic shift) for DMRS (demodulation reference signal) and indexof OC/OCC (orthogonal cover/orthogonal cover code)—this may be formed of3 bits.

9) Uplink index—this may be formed of 2 bits. This field may be presentonly for TDD operation in accordance with an uplink-downlinkconfiguration 0.

10) DAI (Downlink Assignment Index)—this may be formed of 2 bits. Thisfield may be present only for TDD operation in accordance withuplink-downlink configurations 1-6.

11) CSI (Channel State Information) request—this may be formed of 1 or 2bits. In this connection, a 2 bits field may be only applied when anassociated DCI is mapped to a device having one or more downlink cellset thereto by C-RNTI (Cell-RNTI) in a UE specific manner.

12) SRS (Sounding Reference Signal) request—this may be formed of 0 or 1bit. In this connection, this field may be only applied when ascheduling PUSCH is mapped to a device by C-RNTI (Cell-RNTI) in a UEspecific manner.

13) Resource assignment type—this may be formed of 1 bit.

When a number of information bits in the DCI format 0 is smaller than apayload size (including added padding bits) of the DCI format 1A, 0 maybe added to the DCI format 0 such that a number of information bits inthe DCI format 0 is equal to the payload size of the DCI format 1A.

FIG. 4 illustrates a structure of an uplink subframe in the wirelesscommunication system to which the present invention can be applied.

Referring to FIG. 4, the uplink subframe may be divided into the controlregion and the data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) transporting uplink control information isallocated to the control region. A physical uplink shared channel(PUSCH) transporting user data is allocated to the data region. Oneterminal does not simultaneously transmit the PUCCH and the PUSCH inorder to maintain a single carrier characteristic.

A resource block (RB) pair in the subframe are allocated to the PUCCHfor one terminal. RBs included in the RB pair occupy differentsubcarriers in two slots, respectively. The RB pair allocated to thePUCCH frequency-hops in a slot boundary.

Physical Uplink Control Channel (PUCCH)

The uplink control information (UCI) transmitted through the PUCCH mayinclude a scheduling request (SR), HARQ ACK/NACK information, anddownlink channel measurement information.

The HARQ ACK/NACK information may be generated according to a downlinkdata packet on the PDSCH is successfully decoded. In the existingwireless communication system, 1 bit is transmitted as ACK/NACKinformation with respect to downlink single codeword transmission and 2bits are transmitted as the ACK/NACK information with respect todownlink 2-codeword transmission.

The channel measurement information which designates feedbackinformation associated with a multiple input multiple output (MIMO)technique may include a channel quality indicator (CQI), a precodingmatrix index (PMI), and a rank indicator (RI). The channel measurementinformation may also be collectively expressed as the CQI.

20 bits may be used per subframe for transmitting the CQI.

The PUCCH may be modulated by using binary phase shift keying (BPSK) andquadrature phase shift keying (QPSK) techniques. Control information ofa plurality of terminals may be transmitted through the PUCCH and whencode division multiplexing (CDM) is performed to distinguish signals ofthe respective terminals, a constant amplitude zero autocorrelation(CAZAC) sequence having a length of 12 is primary used. Since the CAZACsequence has a characteristic to maintain a predetermined amplitude inthe time domain and the frequency domain, the CAZAC sequence has aproperty suitable for increasing coverage by decreasing apeak-to-average power ratio (PAPR) or cubic metric (CM) of the terminal.Further, the ACK/NACK information for downlink data transmissionperformed through the PUCCH is covered by using an orthogonal sequenceor an orthogonal cover (OC).

Further, the control information transmitted on the PUCCH may bedistinguished by using a cyclically shifted sequence having differentcyclic shift (CS) values. The cyclically shifted sequence may begenerated by cyclically shifting a base sequence by a specific cyclicshift (CS) amount. The specific CS amount is indicated by the cyclicshift (CS) index. The number of usable cyclic shifts may vary dependingon delay spread of the channel. Various types of sequences may be usedas the base sequence the CAZAC sequence is one example of thecorresponding sequence.

Further, the amount of control information which the terminal maytransmit in one subframe may be determined according to the number (thatis, SC-FDMA symbols other an SC-FDMA symbol used for transmitting areference signal (RS) for coherent detection of the PUCCH) of SC-FDMAsymbols which are usable for transmitting the control information.

In the 3GPP LTE system, the PUCCH is defined as a total of 7 differentformats according to the transmitted control information, a modulationtechnique, the amount of control information, and the like and anattribute of the uplink control information (UCI) transmitted accordingto each PUCCH format may be summarized as shown in Table 4 given below.

TABLE 4 PUCCH Format Uplink Control Information(UCI) Format 1 SchedulingRequest(SR)(unmodulated waveform) Format 1a 1-bit HARQ ACK/NACKwith/without SR Format 1b 2-bit HARQ ACK/NACK with/without SR Format 2CQI (20 coded bits) Format 2 CQI and 1- or 2-bit HARQ ACK/NACK (20 bits)for extended CP only Format 2a CQI and 1-bit HARQ ACK/NACK (20 + 1 codedbits) Format 2b CQI and 2-bit HARQ ACK/NACK (20 + 2 coded bits)

PUCCH format 1 is used for transmitting only the SR. A waveform which isnot modulated is adopted in the case of transmitting only the SR andthis will be described below in detail.

PUCCH format 1a or 1b is used for transmitting the HARQ ACK/NACK. PUCCHformat 1a or 1b may be used when only the HARQ ACK/NACK is transmittedin a predetermined subframe. Alternatively, the HARQ ACK/NACK and the SRmay be transmitted in the same subframe by using PUCCH format 1a or 1b.

PUCCH format 2 is used for transmitting the CQI and PUCCH format 2a or2b is used for transmitting the CQI and the HARQ ACK/NACK.

In the case of an extended CP, PUCCH format 2 may be transmitted fortransmitting the CQI and the HARQ ACK/NACK.

FIG. 5 illustrates one example of a type in which PUCCH formats aremapped to a PUCCH region of an uplink physical resource block in thewireless communication system to which the present invention can beapplied.

In FIG. 5, N_(RB) ^(UL) represents the number of resource blocks in theuplink and 0, 1, . . . , N_(RB) ^(UL)−1 mean numbers of physicalresource blocks. Basically, the PUCCH is mapped to both edges of anuplink frequency block. As illustrated in FIG. 5, PUCCH format 2/2a/2bis mapped to a PUCCH region expressed as m=0, 1 and this may beexpressed in such a manner that PUCCH format 2/2a/2b is mapped toresource blocks positioned at a band edge. Further, both PUCCH format2/2a/2b and PUCCH format 1/1a/1b may be mixedly mapped to a PUCCH regionexpressed as m=2. Next, PUCCH format 1/1a/1b may be mapped to a PUCCHregion expressed as m=3, 4, and 5. The number (N_(RB) ⁽²⁾) of PUCCH RBswhich are usable by PUCCH format 2/2a/2b may be indicated to terminalsin the cell by broadcasting signaling.

PUCCH format 2/2a/2b is described. PUCCH format 2/2a/2b is a controlchannel for transmitting channel measurement feedback (CQI, PMI, andRI).

A reporting period of the channel measurement feedbacks (hereinafter,collectively expressed as CQI information) and a frequency wise(alternatively, a frequency resolution) to be measured may be controlledby the base station. In the time domain, periodic and aperiodic CQIreporting may be supported. PUCCH format 2 may be used for only theperiodic reporting and the PUSCH may be used for aperiodic reporting. Inthe case of the aperiodic reporting, the base station may instruct theterminal to transmit a scheduling resource loaded with individual CQIreporting for the uplink data transmission.

FIG. 6 illustrates a structure of a CQI channel in the case of a generalCP in the wireless communication system to which the present inventioncan be applied.

In SC-FDMA symbols 0 to 6 of one slot, SC-FDMA symbols 1 and 5 (secondand sixth symbols) may be used for transmitting a demodulation referencesignal and the CQI information may be transmitted in the residualSC-FDMA symbols. Meanwhile, in the case of the extended CP, one SC-FDMAsymbol (SC-FDMA symbol 3) is used for transmitting the DMRS.

In PUCCH format 2/2a/2b, modulation by the CAZAC sequence is supportedand the CAZAC sequence having the length of 12 is multiplied by aQPSK-modulated symbol. The cyclic shift (CS) of the sequence is changedbetween the symbol and the slot. The orthogonal covering is used withrespect to the DMRS.

The reference signal (DMRS) is loaded on two SC-FDMA symbols separatedfrom each other by 3 SC-FDMA symbols among 7 SC-FDMA symbols included inone slot and the CQI information is loaded on 5 residual SC-FDMAsymbols. Two RSs are used in one slot in order to support a high-speedterminal. Further, the respective terminals are distinguished by usingthe CS sequence. CQI information symbols are modulated and transferredto all SC-FDMA symbols and the SC-FDMA symbol is constituted by onesequence. That is, the terminal modulates and transmits the CQI to eachsequence.

The number of symbols which may be transmitted to one TTI is 10 andmodulation of the CQI information is determined up to QPSK. When QPSKmapping is used for the SC-FDMA symbol, since a CQI value of 2 bits maybe loaded, a CQI value of 10 bits may be loaded on one slot. Therefore,a CQI value of a maximum of 20 bits may be loaded on one subframe. Afrequency domain spread code is used for spreading the CQI informationin the frequency domain.

The CAZAC sequence (for example, ZC sequence) having the length of 12may be used as the frequency domain spread code. CAZAC sequences havingdifferent CS values may be applied to the respective control channels tobe distinguished from each other. IFFT is performed with respect to theCQI information in which the frequency domain is spread.

12 different terminals may be orthogonally multiplexed on the same PUCCHRB by a cyclic shift having 12 equivalent intervals. In the case of ageneral CP, a DMRS sequence on SC-FDMA symbol 1 and 5 (on SC-FDMA symbol3 in the case of the extended CP) is similar to a CQI signal sequence onthe frequency domain, but the modulation of the CQI information is notadopted.

The terminal may be semi-statically configured by upper-layer signalingso as to periodically report different CQI, PMI, and RI types on PUCCHresources indicated as PUCCH resource indexes (n_(PUCCH)^((1,{tilde over (p)})), n_(PUCCH) ^((2,{tilde over (p)})), andn_(PUCCH) ^((3,{tilde over (p)})). Herein, the PUCCH resource index(n_(PUCCH) ^((2,{tilde over (p)})) is information indicating the PUCCHregion used for PUCCH format 2/2a/2b and a CS value to be used.

PUCCH Channel Structure

PUCCH formats 1a and 1b are described.

In PUCCH format 1a and 1b, the CAZAC sequence having the length of 12 ismultiplied by a symbol modulated by using a BPSK or QPSK modulationscheme. For example, a result acquired by multiplying a modulated symbold(0) by a CAZAC sequence r(n) (n=0, 1, 2, . . . , N−1) having a lengthof N becomes y(0), y(1), y(2), . . . , y(N−1). y(0), . . . , y(N−1)symbols may be designated as a block of symbols. The modulated symbol ismultiplied by the CAZAC sequence and thereafter, the block-wise spreadusing the orthogonal sequence is adopted.

A Hadamard sequence having a length of 4 is used with respect to generalACK/NACK information and a discrete Fourier transform (DFT) sequencehaving a length of 3 is used with respect to the ACK/NACK informationand the reference signal.

The Hadamard sequence having the length of 2 is used with respect to thereference signal in the case of the extended CP.

FIG. 7 illustrates a structure of an ACK/NACK channel in the case of ageneral CP in the wireless communication system to which the presentinvention can be applied.

In FIG. 7, a PUCCH channel structure for transmitting the HARQ ACK/NACKwithout the CQI is exemplarily illustrated.

The reference signal (DMRS) is loaded on three consecutive SC-FDMAsymbols in a middle part among 7 SC-FDMA symbols and the ACK/NACK signalis loaded on 4 residual SC-FDMA symbols.

Meanwhile, in the case of the extended CP, the RS may be loaded on twoconsecutive symbols in the middle part. The number of and the positionsof symbols used in the RS may vary depending on the control channel andthe numbers and the positions of symbols used in the ACK/NACK signalassociated with the positions of symbols used in the RS may alsocorrespondingly vary depending on the control channel.

Acknowledgment response information (not scrambled status) of 1 bit and2 bits may be expressed as one HARQ ACK/NACK modulated symbol by usingthe BPSK and QPSK modulation techniques, respectively. A positiveacknowledgement response (ACK) may be encoded as ‘1’ and a negativeacknowledgment response (NACK) may be encoded as ‘0’.

When a control signal is transmitted in an allocated band, 2-dimensional(D) spread is adopted in order to increase a multiplexing capacity. Thatis, frequency domain spread and time domain spread are simultaneouslyadopted in order to increase the number of terminals or control channelswhich may be multiplexed.

A frequency domain sequence is used as the base sequence in order tospread the ACK/NACK signal in the frequency domain. A Zadoff-Chu (ZC)sequence which is one of the CAZAC sequences may be used as thefrequency domain sequence. For example, different CSs are applied to theZC sequence which is the base sequence, and as a result, multiplexingdifferent terminals or different control channels may be applied. Thenumber of CS resources supported in an SC-FDMA symbol for PUCCH RBs forHARQ ACK/NACK transmission is set by a cell-specific upper-layersignaling parameter (Δ_(shift) ^(PUCCH)).

The ACK/NACK signal which is frequency-domain spread is spread in thetime domain by using an orthogonal spreading code. As the orthogonalspreading code, a Walsh-Hadamard sequence or DFT sequence may be used.For example, the ACK/NACK signal may be spread by using an orthogonalsequence (w0, w1, w2, and w3) having the length of 4 with respect to 4symbols. Further, the RS is also spread through an orthogonal sequencehaving the length of 3 or 2. This is referred to as orthogonal covering(OC).

Multiple terminals may be multiplexed by a code division multiplexing(CDM) scheme by using the CS resources in the frequency domain and theOC resources in the time domain described above. That is, ACK/NACKinformation and RSs of a lot of terminals may be multiplexed on the samePUCCH RB.

In respect to the time-domain spread CDM, the number of spreading codessupported with respect to the ACK/NACK information is limited by thenumber of RS symbols. That is, since the number of RS transmittingSC-FDMA symbols is smaller than that of ACK/NACK informationtransmitting SC-FDMA symbols, the multiplexing capacity of the RS issmaller than that of the ACK/NACK information.

For example, in the case of the general CP, the ACK/NACK information maybe transmitted in four symbols and not 4 but 3 orthogonal spreadingcodes are used for the ACK/NACK information and the reason is that thenumber of RS transmitting symbols is limited to 3 to use only 3orthogonal spreading codes for the RS.

In the case of the subframe of the general CP, when 3 symbols are usedfor transmitting the RS and 4 symbols are used for transmitting theACK/NACK information in one slot, for example, if 6 CSs in the frequencydomain and 3 orthogonal cover (OC) resources may be used, HARQacknowledgement responses from a total of 18 different terminals may bemultiplexed in one PUCCH RB. In the case of the subframe of the extendedCP, when 2 symbols are used for transmitting the RS and 4 symbols areused for transmitting the ACK/NACK information in one slot, for example,if 6 CSs in the frequency domain and 2 orthogonal cover (OC) resourcesmay be used, the HARQ acknowledgement responses from a total of 12different terminals may be multiplexed in one PUCCH RB.

Next, PUCCH format 1 is described. The scheduling request (SR) istransmitted by a scheme in which the terminal requests scheduling ordoes not request the scheduling. An SR channel reuses an ACK/NACKchannel structure in PUCCH format 1a/1b and is configured by an on-offkeying (OOK) scheme based on an ACK/NACK channel design. In the SRchannel, the reference signal is not transmitted. Therefore, in the caseof the general CP, a sequence having a length of 7 is used and in thecase of the extended CP, a sequence having a length of 6 is used.Different cyclic shifts (CSs) or orthogonal covers (OCs) may beallocated to the SR and the ACK/NACK. That is, the terminal transmitsthe HARQ ACK/NACK through a resource allocated for the SR in order totransmit a positive SR. The terminal transmits the HARQ ACK/NACK througha resource allocated for the ACK/NACK in order to transmit a negativeSR.

Next, an enhanced-PUCCH (e-PUCCH) format is described. An e-PUCCH maycorrespond to PUCCH format 3 of an LTE-A system. A block spreadingtechnique may be applied to ACK/NACK transmission using PUCCH format 3.

The block spreading technique is a scheme that modulates transmission ofthe control signal by using the SC-FDMA scheme unlike the existing PUCCHformat 1 series or 2 series. As illustrated in FIG. 8, a symbol sequencemay be spread and transmitted on the time domain by using an orthogonalcover code (OCC). The control signals of the plurality of terminals maybe multiplexed on the same RB by using the OCC. In the case of PUCCHformat 2 described above, one symbol sequence is transmitted throughoutthe time domain and the control signals of the plurality of terminalsare multiplexed by using the cyclic shift (CS) of the CAZAC sequence,while in the case of a block spreading based on PUCCH format (forexample, PUCCH format 3), one symbol sequence is transmitted throughoutthe frequency domain and the control signals of the plurality ofterminals are multiplexed by using the time domain spreading using theOCC.

FIG. 8 illustrates one example of generating and transmitting 5 SC-FDMAsymbols during one slot in the wireless communication system to whichthe present invention can be applied.

In FIG. 8, an example of generating and transmitting 5 SC-FDMA symbols(that is, data part) by using an OCC having the length of 5(alternatively, SF=5) in one symbol sequence during one slot. In thiscase, two RS symbols may be used during one slot.

In the example of FIG. 8, the RS symbol may be generated from a CAZACsequence to which a specific cyclic shift value is applied andtransmitted in a type in which a predetermined OCC is applied(alternatively, multiplied) throughout a plurality of RS symbols.Further, in the example of FIG. 8, when it is assumed that 12 modulatedsymbols are used for each OFDM symbol (alternatively, SC-FDMA symbol)and the respective modulated symbols are generated by QPSK, the maximumbit number which may be transmitted in one slot becomes 24 bits (=12×2).Accordingly, the bit number which is transmittable by two slots becomesa total of 48 bits. When a PUCCH channel structure of the blockspreading scheme is used, control information having an extended sizemay be transmitted as compared with the existing PUCCH format 1 seriesand 2 series.

General Carrier Aggregation

A communication environment considered in embodiments of the presentinvention includes multi-carrier supporting environments. That is, amulti-carrier system or a carrier aggregation system used in the presentinvention means a system that aggregates and uses one or more componentcarriers (CCs) having a smaller bandwidth smaller than a target band atthe time of configuring a target wideband in order to support awideband.

In the present invention, multi-carriers mean aggregation of(alternatively, carrier aggregation) of carriers and in this case, theaggregation of the carriers means both aggregation between continuouscarriers and aggregation between non-contiguous carriers. Further, thenumber of component carriers aggregated between the downlink and theuplink may be differently set. A case in which the number of downlinkcomponent carriers (hereinafter, referred to as ‘DL CC’) and the numberof uplink component carriers (hereinafter, referred to as ‘UL CC’) arethe same as each other is referred to as symmetric aggregation and acase in which the number of downlink component carriers and the numberof uplink component carriers are different from each other is referredto as asymmetric aggregation. The carrier aggregation may be usedmixedly with a term such as the carrier aggregation, the bandwidthaggregation, spectrum aggregation, or the like.

The carrier aggregation configured by combining two or more componentcarriers aims at supporting up to a bandwidth of 100 MHz in the LTE-Asystem. When one or more carriers having the bandwidth than the targetband are combined, the bandwidth of the carriers to be combined may belimited to a bandwidth used in the existing system in order to maintainbackward compatibility with the existing IMT system. For example, theexisting 3GPP LTE system supports bandwidths of 1.4, 3, 5, 10, 15, and20 MHz and a 3GPP LTE-advanced system (that is, LTE-A) may be configuredto support a bandwidth larger than 20 MHz by using on the bandwidth forcompatibility with the existing system. Further, the carrier aggregationsystem used in the preset invention may be configured to support thecarrier aggregation by defining a new bandwidth regardless of thebandwidth used in the existing system.

The LTE-A system uses a concept of the cell in order to manage a radioresource.

The carrier aggregation environment may be called a multi-cellenvironment. The cell is defined as a combination of a pair of adownlink resource (DL CC) and an uplink resource (UL CC), but the uplinkresource is not required. Therefore, the cell may be constituted by onlythe downlink resource or both the downlink resource and the uplinkresource. When a specific terminal has only one configured serving cell,the cell may have one DL CC and one UL CC, but when the specificterminal has two or more configured serving cells, the cell has DL CCsas many as the cells and the number of UL CCs may be equal to or smallerthan the number of DL CCs.

Alternatively, contrary to this, the DL CC and the UL CC may beconfigured. That is, when the specific terminal has multiple configuredserving cells, a carrier aggregation environment having UL CCs more thanDL CCs may also be supported. That is, the carrier aggregation may beappreciated as aggregation of two or more cells having different carrierfrequencies (center frequencies). Herein, the described ‘cell’ needs tobe distinguished from a cell as an area covered by the base stationwhich is generally used.

The cell used in the LTE-A system includes a primary cell (PCell) and asecondary cell (SCell. The P cell and the S cell may be used as theserving cell. In a terminal which is in an RRC_CONNECTED state, but doesnot have the configured carrier aggregation or does not support thecarrier aggregation, only one serving constituted by only the P cell ispresent. On the contrary, in a terminal which is in the RRC_CONNECTEDstate and has the configured carrier aggregation, one or more servingcells may be present and the P cell and one or more S cells are includedin all serving cells.

The serving cell (P cell and S cell) may be configured through an RRCparameter. PhysCellId as a physical layer identifier of the cell hasinteger values of 0 to 503. SCellIndex as a short identifier used toidentify the S cell has integer values of 1 to 7. ServCellIndex as ashort identifier used to identify the serving cell (P cell or S cell)has the integer values of 0 to 7. The value of 0 is applied to the Pcell and SCellIndex is previously granted for application to the S cell.That is, a cell having a smallest cell ID (alternatively, cell index) inServCellIndex becomes the P cell.

The P cell means a cell that operates on a primary frequency(alternatively, primary CC). The terminal may be used to perform aninitial connection establishment process or a connectionre-establishment process and may be designated as a cell indicatedduring a handover process. Further, the P cell means a cell whichbecomes the center of control associated communication among servingcells configured in the carrier aggregation environment. That is, theterminal may be allocated with and transmit the PUCCH only in the P cellthereof and use only the P cell to acquire the system information orchange a monitoring procedure. An evolved universal terrestrial radioaccess (E-UTRAN) may change only the P cell for the handover procedureto the terminal supporting the carrier aggregation environment by usingan RRC connection reconfiguration message (RRCConnectionReconfigutaion)message of an upper layer including mobile control information(mobilityControlInfo).

The S cell means a cell that operates on a secondary frequency(alternatively, secondary CC). Only one P cell may be allocated to aspecific terminal and one or more S cells may be allocated to thespecific terminal. The S cell may be configured after RRC connectionestablishment is achieved and used for providing an additional radioresource. The PUCCH is not present in residual cells other than the Pcell, that is, the S cells among the serving cells configured in thecarrier aggregation environment. The E-UTRAN may provide all systeminformation associated with a related cell which is in an RRC_CONNECTEDstate through a dedicated signal at the time of adding the S cells tothe terminal that supports the carrier aggregation environment. A changeof the system information may be controlled by releasing and adding therelated S cell and in this case, the RRC connection reconfiguration(RRCConnectionReconfigutaion) message of the upper layer may be used.The E-UTRAN may perform having different parameters for each terminalrather than broadcasting in the related S cell.

After an initial security activation process starts, the E-UTRAN addsthe S cells to the P cell initially configured during the connectionestablishment process to configure a network including one or more Scells. In the carrier aggregation environment, the P cell and the S cellmay operate as the respective component carriers. In an embodimentdescribed below, the primary component carrier (PCC) may be used as thesame meaning as the P cell and the secondary component carrier (SCC) maybe used as the same meaning as the S cell.

FIG. 9 illustrates examples of a component carrier and carrieraggregation in the wireless communication system to which the presentinvention can be applied.

FIG. 9a illustrates a single carrier structure used in an LTE system.The component carrier includes the DL CC and the UL CC. One componentcarrier may have a frequency range of 20 MHz.

FIG. 9b illustrates a carrier aggregation structure used in the LTEsystem. In the case of FIG. 9b , a case is illustrated, in which threecomponent carriers having a frequency magnitude of 20 MHz are combined.Each of three DL CCs and three UL CCs is provided, but the number of DLCCs and the number of UL CCs are not limited. In the case of carrieraggregation, the terminal may simultaneously monitor three CCs, andreceive downlink signal/data and transmit uplink signal/data.

When N DL CCs are managed in a specific cell, the network may allocate M(MN) DL CCs to the terminal. In this case, the terminal may monitor onlyM limited DL CCs and receive the DL signal. Further, the network gives L(L≤M≤N) DL CCs to allocate a primary DL CC to the terminal and in thiscase, UE needs to particularly monitor L DL CCs. Such a scheme may besimilarly applied even to uplink transmission.

A linkage between a carrier frequency (alternatively, DL CC) of thedownlink resource and a carrier frequency (alternatively, UL CC) of theuplink resource may be indicated by an upper-layer message such as theRRC message or the system information. For example, a combination of theDL resource and the UL resource may be configured by a linkage definedby system information block type 2 (SIB2). In detail, the linkage maymean a mapping relationship between the DL CC in which the PDCCHtransporting a UL grant and a UL CC using the UL grant and mean amapping relationship between the DL CC (alternatively, UL CC) in whichdata for the HARQ is transmitted and the UL CC (alternatively, DL CC) inwhich the HARQ ACK/NACK signal is transmitted.

Cross Carrier Scheduling

In the carrier aggregation system, in terms of scheduling for thecarrier or the serving cell, two types of a self-scheduling method and across carrier scheduling method are provided. The cross carrierscheduling may be called cross component carrier scheduling or crosscell scheduling.

The cross carrier scheduling means transmitting the PDCCH (DL grant) andthe PDSCH to different respective DL CCs or transmitting the PUSCHtransmitted according to the PDCCH (UL grant) transmitted in the DL CCthrough other UL CC other than a UL CC linked with the DL CC receivingthe UL grant.

Whether to perform the cross carrier scheduling may be UE-specificallyactivated or deactivated and semi-statically known for each terminalthrough the upper-layer signaling (for example, RRC signaling).

When the cross carrier scheduling is activated, a carrier indicatorfield (CIF) indicating through which DL/UL CC the PDSCH/PUSCH thePDSCH/PUSCH indicated by the corresponding PDCCH is transmitted isrequired. For example, the PDCCH may allocate the PDSCH resource or thePUSCH resource to one of multiple component carriers by using the CIF.That is, the CIF is set when the PDSCH or PUSCH resource is allocated toone of DL/UL CCs in which the PDCCH on the DL CC is multiply aggregated.In this case, a DCI format of LTE-A Release-8 may extend according tothe CIF. In this case, the set CIF may be fixed to a 3-bit field and theposition of the set CIF may be fixed regardless of the size of the DCIformat. Further, a PDCCH structure (the same coding and the same CCEbased resource mapping) of the LTE-A Release-8 may be reused.

On the contrary, when the PDCCH on the DL CC allocates the PDSCHresource on the same DL CC or allocates the PUSCH resource on a UL CCwhich is singly linked, the CIF is not set. In this case, the same PDCCHstructure (the same coding and the same CCE based resource mapping) andDCI format as the LTE-A Release-8 may be used.

When the cross carrier scheduling is possible, the terminal needs tomonitor PDCCHs for a plurality of DCIs in a control region of amonitoring CC according to a transmission mode and/or a bandwidth foreach CC. Therefore, a configuration and PDCCH monitoring of a searchspace which may support monitoring the PDCCHs for the plurality of DCIsare required.

In the carrier aggregation system, a terminal DL CC aggregate representsan aggregate of DL CCs in which the terminal is scheduled to receive thePDSCH and a terminal UL CC aggregate represents an aggregate of UL CCsin which the terminal is scheduled to transmit the PUSCH. Further, aPDCCH monitoring set represents a set of one or more DL CCs that performthe PDCCH monitoring. The PDCCH monitoring set may be the same as theterminal DL CC set or a subset of the terminal DL CC set. The PDCCHmonitoring set may include at least any one of DL CCs in the terminal DLCC set. Alternatively, the PDCCH monitoring set may be definedseparately regardless of the terminal DL CC set. The DL CCs included inthe PDCCH monitoring set may be configured in such a manner thatself-scheduling for the linked UL CC is continuously available. Theterminal DL CC set, the terminal UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

When the cross carrier scheduling is deactivated, the deactivation ofthe cross carrier scheduling means that the PDCCH monitoring setcontinuously means the terminal DL CC set and in this case, anindication such as separate signaling for the PDCCH monitoring set isnot required. However, when the cross carrier scheduling is activated,the PDCCH monitoring set is preferably defined in the terminal DL CCset. That is, the base station transmits the PDCCH through only thePDCCH monitoring set in order to schedule the PDSCH or PUSCH for theterminal.

FIG. 10 illustrates one example of a subframe structure depending oncross carrier scheduling in the wireless communication system to whichthe present invention can be applied.

Referring to FIG. 10, a case is illustrated, in which three DL CCs areassociated with a DL subframe for an LTE-A terminal and DL CC′A′ isconfigured as a PDCCH monitoring DL CC. When the CIF is not used, eachDL CC may transmit the PDCCH scheduling the PDSCH thereof without theCIF. On the contrary, when the CIF is used through the upper-layersignaling, only one DL CC ‘A’ may transmit the PDCCH scheduling thePDSCH thereof or the PDSCH of another CC by using the CIF. In this case,DL CC ‘13’ and ‘C’ in which the PDCCH monitoring DL CC is not configureddoes not transmit the PDCCH.

General ACK/NACK Multiplexing Method

In a situation in which the terminal simultaneously needs to transmitmultiple ACKs/NACKs corresponding to multiple data units received froman eNB, an ACK/NACK multiplexing method based on PUCCH resourceselection may be considered in order to maintain a single-frequencycharacteristic of the ACK/NACK signal and reduce ACK/NACK transmissionpower.

Together with ACK/NACK multiplexing, contents of ACK/NACK responses formultiple data units may be identified by combining a PUCCH resource anda resource of QPSK modulation symbols used for actual ACK/NACKtransmission.

For example, when one PUCCH resource may transmit 4 bits and four dataunits may be maximally transmitted, an ACK/NACK result may be identifiedin the eNB as shown in Table 5 given below.

TABLE 5 HARQ-ACK(0), HARQ-ACK(1), HARQ-ACK(2), b(0), HARQ-ACK(3)n_(PUCCH) ⁽¹⁾ b(1) ACK, ACK, ACK, ACK n_(PUCCH,1) ⁽¹⁾ 1, 1 ACK, ACK,ACK, NACK/DTX n_(PUCCH,1) ⁽¹⁾ 1, 0 NACK/DTX, NACK/DTX, NACK, DTXn_(PUCCH,2) ⁽¹⁾ 1, 1 ACK, ACK, NACK/DTX, ACK n_(PUCCH,1) ⁽¹⁾ 1, 0 NACK,DTX, DTX, DTX n_(PUCCH,0) ⁽¹⁾ 1, 0 ACK, ACK, NACK/DTX, NACK/DTXn_(PUCCH,1) ⁽¹⁾ 1, 0 ACK, NACK/DTX, ACK, ACK n_(PUCCH,3) ⁽¹⁾ 0, 1NACK/DTX, NACK/DTX, NACK/DTX, NACK n_(PUCCH,3) ⁽¹⁾ 1, 1 ACK, NACK/DTX,ACK, NACK/DTX n_(PUCCH,2) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, ACKn_(PUCCH,0) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, NACK/DTX n_(PUCCH,0) ⁽¹⁾1, 1 NACK/DTX, ACK, ACK, ACK n_(PUCCH,3) ⁽¹⁾ 0, 1 NACK/DTX, NACK, DTX,DTX n_(PUCCH,1) ⁽¹⁾ 0, 0 NACK/DTX, ACK, ACK, NACK/DTX n_(PUCCH,2) ⁽¹⁾ 1,0 NACK/DTX, ACK, NACK/DTX, ACK n_(PUCCH,3) ⁽¹⁾ 1, 0 NACK/DTX, ACK,NACK/DTX, NACK/DTX n_(PUCCH,1) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, ACKn_(PUCCH,3) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, NACK/DTX n_(PUCCH,2) ⁽¹⁾0, 0 NACK/DTX, NACK/DTX, NACK/DTX, ACK n_(PUCCH,3) ⁽¹⁾ 0, 0 DTX, DTX,DTX, DTX N/A N/A

In Table 5 given above, HARQ-ACK(i) represents an ACK/NACK result for ani-th data unit. In Table 5 given above, discontinuous transmission (DTX)means that there is no data unit to be transmitted for the correspondingHARQ-ACK(i) or that the terminal may not detect the data unitcorresponding to the HARQ-ACK(i).

According to Table 5 given above, a maximum of four PUCCH resources(n_(PUCCH,0) ⁽¹⁾, n_(PUCCH,1) ⁽¹⁾, n_(PUCCH,2) ⁽¹⁾, and n_(PUCCH,3)) ⁽¹⁾are provided and b(0) and b(1) are two bits transmitted by using aselected PUCCH.

For example, when the terminal successfully receives all of four dataunits, the terminal transmits 2 bits (1,1) by using n_(PUCCH,1) ⁽¹⁾.

When the terminal fails to decoding in first and third data units andsucceeds in decoding in second and fourth data units, the terminaltransmits bits (1,0) by using n_(PUCCH,3) ⁽¹⁾.

In ACK/NACK channel selection, when there is at least one ACK, the NACKand the DTX are coupled with each other. The reason is that acombination of the PUCCH resource and the QPSK symbol may not allACK/NACK states. However, when there is no ACK, the DTX is decoupledfrom the NACK.

In this case, the PUCCH resource linked to the data unit correspondingto one definite NACK may also be reserved to transmit signals ofmultiple ACKs/NACKs.

Validation of PDCCH for Semi-Persistent Scheduling

Semi-persistent scheduling (SPS) is a scheduling scheme that allocatesthe resource to the terminal to be persistently maintained during aspecific time interval.

When a predetermined amount of data is transmitted for a specific timelike a voice over Internet protocol (VoIP), since the controlinformation need not be transmitted every data transmission interval forthe resource allocation, the waste of the control information may bereduced by using the SPS scheme. In a so-called semi-persistentscheduling (SPS) method, a time resource domain in which the resourcemay be allocated to the terminal is preferentially allocated.

In this case, in a semi-persistent allocation method, a time resourcedomain allocated to a specific terminal may be configured to haveperiodicity. Then, a frequency resource domain is allocated as necessaryto complete allocation of the time-frequency resource. Allocating thefrequency resource domain may be designated as so-called activation.When the semi-persistent allocation method is used, since the resourceallocation is maintained during a predetermined period by one-timesignaling, the resource need not be repeatedly allocated, and as aresult, signaling overhead may be reduced.

Thereafter, since the resource allocation to the terminal is notrequired, signaling for releasing the frequency resource allocation maybe transmitted from the base station to the terminal. Releasing theallocation of the frequency resource domain may be designated asdeactivation.

In current LTE, in which subframes the SPS is first transmitted/receivedthrough radio resource control (RRC) signaling for the SPS for theuplink and/or downlink is announced to the terminal. That is, the timeresource is preferentially designated among the time and frequencyresources allocated for the SPS through the RRC signaling. In order toannounce a usable subframe, for example, a period and an offset of thesubframe may be announced. However, since the terminal is allocated withonly the time resource domain through the RRC signaling, even though theterminal receives the RRC signaling, the terminal does not immediatelyperform transmission and reception by the SPS and the terminal allocatesthe frequency resource domain as necessary to complete the allocation ofthe time-frequency resource. Allocating the frequency resource domainmay be designated as deactivation and releasing the allocation of thefrequency resource domain may be designated as deactivation.

Therefore, the terminal receives the PDCCH indicating the activation andthereafter, allocate the frequency resource according to RB allocationinformation included in the received PDCCH and applies modulation andcode rate depending on modulation and coding scheme (MCS) information tostart transmission and reception according to the period and the offsetof the subframe allocated through the RRC signaling.

Next, when the terminal receives the PDCCH announcing the deactivationfrom the base station, the terminal stops transmission and reception.When the terminal receives the PDCCH indicating the activation orreactivation after stopping the transmission and reception, the terminalresumes the transmission and reception again with the period and theoffset of the subframe allocated through the RRC signaling by using theRC allocation, the MCS, and the like designated by the PDCCH. That is,the time resource is performed through the RRC signaling, but the signalmay be actually transmitted and received after receiving the PDCCHindicating the activation and reactivation of the SPS and the signaltransmission and reception stop after receiving the PDCCH indicating thedeactivation of the SPS.

When all conditions described below are satisfied, the terminal mayvalidate a PDCCH including an SPS indication. First, a CRC parity bitadded for a PDCCH payload needs to be scrambled with an SPS C-RNTI andsecond, a new data indicator (NDI) field needs to be set to 0. Herein,in the case of DCI formats 2, 2A, 2B, and 2C, the new data indicatorfield indicates one activated transmission block.

In addition, when each field used in the DCI format is set according toTables 6 and 7 given below, the validation is completed. When thevalidation is completed, the terminal recognizes that received DCIinformation is valid SPS activation or deactivation (alternatively,release). On the contrary, when the validation is not completed, theterminal recognizes that a non-matching CRC is included in the receivedDCI format.

Table 6 shows a field for validating the PDCCH indicating the SPSactivation.

TABLE 6 DCI DCI format format 0 1/1A DCI format 2/2A/2B TPC command forset to ‘00’ N/A N/A scheduled PUSCH Cyclic shift DM RS set to N/A N/A‘000’ Modulation and coding MSB is N/A N/A scheme and redundancy set to‘0’ version HARQ process number N/A FDD: set FDD: set to ‘000’ to ‘000’TDD: set to ‘0000’ TDD: set to ‘0000’ Modulation and coding N/A MSB isFor the enabled scheme set to ‘0’ transport block: MSB is set to ‘0’Redundancy version N/A set to ‘00’ For the enabled transport block: setto ‘00’

Table 7 shows a field for validating the PDCCH indicating the SPSdeactivation (alternatively, release).

TABLE 7 DCI format 0 DCI format 1A TPC command for scheduled set to ‘00’N/A PUSCH Cyclic shift DM RS set to ‘000’ N/A Modulation and codingscheme and set to ‘11111’ N/A redundancy version Resource blockassignment and Set to all ‘1’s N/A hopping resource allocation HARQprocess number N/A FDD: set to ‘000’ TDD: set to ‘0000’ Modulation andcoding scheme N/A set to ‘11111’ Redundancy version N/A set to ‘00’Resource block assignment N/A Set to all ‘1’s

When the DCI format indicates SPS downlink scheduling activation, a TPCcommand value for the PUCCH field may be used as indexes indicating fourPUCCH resource values set by the upper layer.

PUCCH Piggybacking in Rel-8 LTE

FIG. 11 illustrates one example of transport channel processing of aUL-SCH in the wireless communication system to which the presentinvention can be applied.

In a 3GPP LTE system (=E-UTRA, Rel. 8), in the case of the UL, singlecarrier transmission having an excellent peak-to-average power ratio(PAPR) or cubic metric (CM) characteristic which influences theperformance of a power amplifier is maintained for efficient utilizationof the power amplifier of the terminal. That is, in the case oftransmitting the PUSCH of the existing LTE system, data to betransmitted may maintain the single carrier characteristic throughDFT-precoding and in the case of transmitting the PUCCH, information istransmitted while being loaded on a sequence having the single carriercharacteristic to maintain the single carrier characteristic. However,when the data to be DFT-precoded is non-contiguously allocated to afrequency axis or the PUSCH and the PUCCH are simultaneouslytransmitted, the single carrier characteristic deteriorates. Therefore,when the PUSCH is transmitted in the same subframe as the transmissionof the PUCCH as illustrated in FIG. 11, uplink control information (UCI)to be transmitted to the PUCCH is transmitted (piggyback) together withdata through the PUSCH.

Since the PUCCH and the PUSCH may not be simultaneously transmitted asdescribed above, the existing LTE terminal uses a method thatmultiplexes uplink control information (UCI) (CQI/PMI, HARQ-ACK, RI, andthe like) to the PUSCH region in a subframe in which the PUSCH istransmitted.

As one example, when the channel quality indicator (CQI) and/orprecoding matrix indicator (PMI) needs to be transmitted in a subframeallocated to transmit the PUSCH, UL-SCH data and the CQI/PMI aremultiplexed after DFT-spreading to transmit both control information anddata. In this case, the UL-SCH data is rate-matched by considering aCQI/PMI resource. Further, a scheme is used, in which the controlinformation such as the HARQ ACK, the RI, and the like punctures theUL-SCH data to be multiplexed to the PUSCH region.

FIG. 12 illustrates one example of a signal processing process of anuplink share channel of a transport channel in the wirelesscommunication system to which the present invention can be applied.

Herein, the signal processing process of the uplink share channel(hereinafter, referred to as “UL-SCH”) may be applied to one or moretransport channels or control information types.

Referring to FIG. 12, the UL-SCH transfers data to a coding unit in theform of a transport block (TB) once every a transmission time interval(TTI).

A CRC parity bit p₀, p₁, p₂, p₃, . . . , p_(L-1) is attached to a bit ofthe transport block received from the upper layer (S120). In this case,A represents the size of the transport block and L represents the numberof parity bits. Input bits to which the CRC is attached are shown in b₀,b₁, b₂, b₃, . . . , b_(B-1) In this case, B represents the number ofbits of the transport block including the CRC.

b₀, b₁, b₂, b₃, . . . , b_(B-1) is segmented into multiple code blocks(CBs) according to the size of the TB and the CRC is attached tomultiple segmented CBs (S121). Bits after the code block segmentationand the CRC attachment are shown in c_(r0), c_(r1), c_(r2), c_(r3), . .. , c_(r(K) _(r) ⁻¹⁾ Herein, r represents No. (r=0, . . . , C−1) of thecode block and Kr represents the bit number depending on the code blockr. Further, C represents the total number of code blocks.

Subsequently, channel coding is performed (S122). Output bits after thechannel coding are shown in d_(r0) ^((i)), d_(r1) ^((i)), d_(r2) ^((i)),d_(r3) ^((i)), . . . , d_(r(D) _(r) ⁻¹⁾ ^((i)). In this case, irepresents an encoded stream index and may have a value of 0, 1, or 2.Dr represents the number of bits of the i-th encoded stream for the codeblock r. r represents the code block number (r=0, . . . , C−1) and Crepresents the total number of code blocks. Each code block may beencoded by turbo coding.

Subsequently, rate matching is performed (S123). Bits after the ratematching are shown in e_(r0), e_(r1), e_(r2), e_(r3), . . . , e_(r(E)_(r) ⁻¹⁾. In this case, r represents the code block number (r=0, . . . ,C−1) and C represents the total number of code blocks. Er represents thenumber of rate-matched bits of the r-th code block.

Subsequently, concatenation among the code blocks is performed again(S124). Bits after the concatenation of the code blocks is performed areshown in f₀, f₁, f₂, f₃, . . . , f_(G-1) In this case, G represents thetotal number of bits encoded for transmission and when the controlinformation is multiplexed with the UL-SCH, the number of bits used fortransmitting the control information is not included.

Meanwhile, when the control information is transmitted in the PUSCH,channel coding of the CQI/PMI, the RI, and the ACK/NACK which are thecontrol information is independently performed (S126, S127, and S128).Since different encoded symbols are allocated for transmitting eachcontrol information, the respective control information has differentcoding rates.

In time division duplex (TDD), as an ACK/NACK feedback mode, two modesof ACK/NACK bundling and ACK/NACK multiplexing are supported by anupper-layer configuration. ACK/NACK information bits for the ACK/NACKbundling are constituted by 1 bit or 2 bits and ACK/NACK informationbits for the ACK/NACK multiplexing are constituted by 1 to 4 bits.

After the concatenation among the code blocks in step S134, encoded bitsf₀, f₁, f₂, f₃, . . . , f_(G-1) of the UL-SCH data and encoded bits q₀,q₁, q₂, q₃, . . . , q_(N) _(L) _(−Q) _(CQI) ⁻¹ of the CQI/PMI aremultiplexed (S125). A multiplexed result of the data and the CQI/PMI isshown in g₀, g₁, g₂, g₃, . . . g_(H′−1). In this case, g_(i) (i=0, . . ., H′−1) represents a column vector having a length of (Q_(m)·N_(L)).H=(G+N_(L)·Q_(CQI)) and H′=H/(N_(L)·Q_(m)). N_(L) represents the numberof layers mapped to a UL-SCH transport block and H represents the totalnumber of encoded bits allocated to N_(L) transport layers mapped withthe transport block for the UL-SCH data and the CQI/PMI information.

Subsequently, the multiplexed data and CQI/PMI, a channel encoded RI,and the ACK/NACK are channel-interleaved to generate an output signal(S129).

Multi-Input Multi-Output (MIMO)

An MIMO technology uses multiple transmitting (Tx) antennas and multiplereceiving (Rx) antennas by breaking from generally one transmittingantenna and one receiving antenna up to now. In other words, the MIMOtechnology is a technology for achieving capacity increment orcapability enhancement by using a multiple input multiple output antennaat a transmitter side or a receiver side of the wireless communicationsystem. Hereinafter, “MIMO” will be referred to as “multiple inputmultiple output antenna”.

In more detail, the MIMO technology does not depend on one antenna pathin order to receive one total message and completes total data bycollecting a plurality of data pieces received through multipleantennas. Consequently, the MIMO technology may increase a data transferrate within in a specific system range and further, increase the systemrange through a specific data transfer rate.

In next-generation mobile communication, since a still higher datatransfer rate than the existing mobile communication is required, it isanticipated that an efficient multiple input multiple output technologyis particularly required. In such a situation, an MIMO communicationtechnology is a next-generation mobile communication technology whichmay be widely used in a mobile communication terminal and a relay andattracts a concern as a technology to overcome a limit of a transmissionamount of another mobile communication according to a limit situationdue to data communication extension, and the like.

Meanwhile, the multiple input multiple output (MIMO) technology amongvarious transmission efficiency improvement technologies which have beenresearched in recent years as a method that may epochally improve acommunication capacity and transmission and reception performancewithout additional frequency allocation or power increment has thelargest attention in recent years.

FIG. 13 is a configuration diagram of a general multiple input multipleoutput (MIMO) communication system.

Referring to FIG. 13, when the number of transmitting antennas increasesto NT and the number of receiving antennas increases to NR at the sametime, since a theoretical channel transmission capacity increases inproportion to the number of antennas unlike a case using multipleantennas only in a transmitter or a receiver, a transfer rate may beimproved and frequency efficiency may be epchally improved. In thiscase, the transfer rate depending on an increase in channel transmissioncapacity may theoretically increase to a value acquired by multiplying amaximum transfer rate (Ro) in the case using one antenna by a rateincrease rate (Ri) given below.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

That is, for example, in an MIMO communication system using fourtransmitting antennas and four receiving antennas, a transfer rate whichis four times higher than a single antenna system may be acquired.

Such an MIMO antenna technology may be divided into a spatial diversityscheme increasing transmission reliability by using symbols passingthrough various channel paths and a spatial multiplexing schemeimproving the transfer rate by simultaneously transmitting multiple datasymbols by using multiple transmitting antennas. Further, a researchinto a scheme that intends to appropriately acquire respectiveadvantages by appropriately combining two schemes is also a field whichhas been researched in recent years.

The respective schemes will be described below in more detail.

First, the spatial diversity scheme includes a space-time block codingseries and a space-time Trelis coding series scheme simultaneously usinga diversity gain and a coding gain. In general, the Trelis is excellentin bit error rate enhancement performance and code generation degree offreedom, but the space-time block code is simple in operationalcomplexity. In the case of such a spatial diversity gain, an amountcorresponding to a multiple (NT×NR) of the number (NT) of transmittingantennas and the number (NR) of receiving antennas may be acquired.

Second, the spatial multiplexing technique is a method that transmitsdifferent data arrays in the respective transmitting antennas and inthis case, mutual interference occurs among data simultaneouslytransmitted from the transmitter in the receiver. The receiver receivesthe data after removing the interference by using an appropriate signalprocessing technique. A noise removing scheme used herein includes amaximum likelihood detection (MLD) receiver, a zero-forcing (ZF)receiver, a minimum mean square error (MMSE) receiver, a diagonal-belllaboratories layered space-time (D-BLAST), a vertical-bell laboratorieslayered space-time), and the like and in particular, when channelinformation may be known in the transmitter side, a singular valuedecomposition (SVD) scheme, and the like may be used.

Third, a technique combining the space diversity and the spatialmultiplexing may be provided. When only the spatial diversity gain isacquired, the performance enhancement gain depending on an increase indiversity degree is gradually saturated and when only the spatialmultiplexing gain is acquired, the transmission reliability deterioratesin the radio channel. Schemes that acquire both two gains while solvingthe problem have been researched and the schemes include a space-timeblock code (Double-STTD), a space-time BICM (STBICM), and the like.

In order to describe a communication method in the MIMO antenna systemdescribed above by a more detailed method, when the communication methodis mathematically modeled, the mathematical modeling may be shown asbelow.

First, it is assumed that NT transmitting antennas and NR receivingantennas are present as illustrated in FIG. 13.

First, in respect to a transmission signal, when NT transmittingantennas are provided, since the maximum number of transmittableinformation is NT, NT may be expressed as a vector given below.s=[s ₁ ,s ₂ , . . . ,s _(N) _(T) ]^(T)  [Equation 2]

Meanwhile, transmission power may be different in the respectivetransmission information s1, s2, . . . , sNT and in this case, when therespective transmission power is P1, P2, . . . , PNT, the transmissioninformation of which the transmission power is adjusted may be expressedas a vector given below.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

Further, ŝ may be expressed as described below as a diagonal matrix P ofthe transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Meanwhile, the information vector of ŝ which the transmission power isadjusted is multiplied by a weight matrix W to constitute NTtransmission signals x1, x2, . . . , xNT which are actually transmitted.Herein, the weight matrix serves to appropriately distribute thetransmission information to the respective antennas according to atransmission channel situation, and the like. The transmission signalsx1, x2, . . . , xNT may be expressed as below by using a vector x.

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {\quad{{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}}} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Herein, wij represents a weight between the i-th transmitting antennaand j-th transmission information and W represents the weight as thematrix. The matrix W is called a weight matrix or a precoding matrix.

Meanwhile, the transmission signal x described above may be divided intotransmission signals in a case using the spatial diversity and a caseusing the spatial multiplexing.

In the case using the spatial multiplexing, since different signals aremultiplexed and sent, all elements of an information vector s havedifferent values, while when the spatial diversity is used, since thesame signal is sent through multiple channel paths, all of the elementsof the information vector s have the same value.

Of course, a method mixing the spatial multiplexing and the spatialdiversity may also be considered. That is, for example, a case may alsobe considered, which transmits the same signal by using the spatialdiversity through three transmitting antennas and different signals aresent by the spatial multiplexing through residual transmitting antennas.

Next, when NR receiving antennas are provided, received signals y1, y2,. . . , yNR of the respective antennas are expressed as a vector y asdescribed below.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

Meanwhile, in the case of modeling the channel in the MIMO antennacommunication system, respective channels may be distinguished accordingto transmitting and receiving antenna indexes and a channel passingthrough a receiving antenna i from a transmitting antenna j will berepresented as hij. Herein, it is noted that in the case of the order ofthe index of hij, the receiving antenna index is earlier and thetransmitting antenna index is later.

The multiple channels are gathered into one to be expressed even asvector and matrix forms. An example of expression of the vector will bedescribed below.

FIG. 14 is a diagram illustrating a channel from multiple transmittingantennas to one receiving antenna.

As illustrated in FIG. 14, a channel which reaches receiving antenna Ifrom a total of NT transmitting antennas may be expressed as below.h _(i) ^(T) =└h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ┘  [Equation 7]

Further, all of channels passing through NR receiving antennas from NTtransmitting antennas may be shown as below through matrix expressionshown in Equation given above.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = {\quad\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Meanwhile, since additive white Gaussian noise (AWGN) is added afterpassing through a channel matrix H given above in an actual channel,white noises n1, n2, . . . , nNR added to NR receiving antennas,respectively are expressed as below.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

Each of the transmission signal, the reception signal, the channel, andthe white noise in the MIMO antenna communication system may beexpressed through a relationship given below by modeling thetransmission signal, the reception signal, the channel, and the whitenoise.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {\quad{{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}}} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

The numbers of rows and columns of the channel matrix H representing thestate of the channel are determined by the numbers of transmitting andreceiving antennas. In the case of the channel matrix H, the number ofrows becomes equivalent to NR which is the number of receiving antennasand the number of columns becomes equivalent to NR which is the numberof transmitting antennas. That is, the channel matrix H becomes an NR×NRmatrix.

In general, a rank of the matrix is defined as the minimum number amongthe numbers of independent rows or columns. Therefore, the rank of thematrix may not be larger than the number of rows or columns. As anequation type example, the rank (rank(H)) of the channel matrix H islimited as below.rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

Further, when the matrix is subjected to Eigen value decomposition, therank may be defined as not 0 but the number of Eigen values among theEigen values. By a similar method, when the rank is subjected tosingular value decomposition, the rank may be defined as not 0 but thenumber of singular values. Accordingly, a physical meaning of the rankin the channel matrix may be the maximum number which may send differentinformation in a given channel.

In the present specification, a ‘rank’ for MIMO transmission representsthe number of paths to independently transmit the signal at a specifictime and in a specific frequency resource and ‘the number of layers’represents the number of signal streams transmitted through each path.In general, since the transmitter side transmits layers of the numbercorresponding to the number of ranks used for transmitting the signal,the rank has the same meaning as the number layers if not particularlymentioned.

Reference Signal (RS)

In the wireless communication system, since the data is transmittedthrough the radio channel, the signal may be distorted duringtransmission. In order for the receiver side to accurately receive thedistorted signal, the distortion of the received signal needs to becorrected by using channel information. In order to detect the channelinformation, a signal transmitting method know by both the transmitterside and the receiver side and a method for detecting the channelinformation by using an distortion degree when the signal is transmittedthrough the channel are primarily used. The aforementioned signal isreferred to as a pilot signal or a reference signal (RS).

When the data is transmitted and received by using the MIMO antenna, achannel state between the transmitting antenna and the receiving antennaneed to be detected in order to accurately receive the signal.Therefore, the respective transmitting antennas need to have individualreference signals.

The downlink reference signal includes a common RS (CRS) shared by allterminals in one cell and a dedicated RS (DRS) for a specific terminal.Information for demodulation and channel measurement may be provided byusing the reference signals.

The receiver side (that is, terminal) measures the channel state fromthe CRS and feeds back the indicators associated with the channelquality, such as the channel quality indicator (CQI), the precodingmatrix index (PMI), and/or the rank indicator (RI) to the transmittingside (that is, base station). The CRS is also referred to as acell-specific RS. On the contrary, a reference signal associated with afeed-back of channel state information (CSI) may be defined as CSI-RS.

The DRS may be transmitted through resource elements when datademodulation on the PDSCH is required. The terminal may receive whetherthe DRS is present through the upper layer and is valid only when thecorresponding PDSCH is mapped. The DRS may be referred to as theUE-specific RS or the demodulation RS (DMRS).

FIG. 15 illustrates a reference signal pattern mapped to a downlinkresource block pair in the wireless communication system to which thepresent invention can be applied.

Referring to FIG. 15, as a wise in which the reference signal is mapped,the downlink resource block pair may be expressed by one subframe in thetimedomain×12 subcarriers in the frequency domain. That is, one resourceblock pair has a length of 14 OFDM symbols in the case of a normalcyclic prefix (CP) (FIG. 15a ) and a length of 12 OFDM symbols in thecase of an extended cyclic prefix (CP) (FIG. 15b ). Resource elements(REs) represented as ‘0’, ‘1’, ‘2’, and ‘3’ in a resource block latticemean the positions of the CRSs of antenna port indexes ‘0’, ‘1’, ‘2’,and ‘3’, respectively and resource elements represented as ‘D’ means theposition of the DRS.

Hereinafter, when the CRS is described in more detail, the CRS is usedto estimate a channel of a physical antenna and distributed in a wholefrequency band as the reference signal which may be commonly received byall terminals positioned in the cell. Further, the CRS may be used todemodulate the channel quality information (CSI) and data.

The CRS is defined as various formats according to an antenna array atthe transmitter side (base station). The 3GPP LTE system (for example,release-8) supports various antenna arrays and a downlink signaltransmitting side has three types of antenna arrays of three singletransmitting antennas, two transmitting antennas, and four transmittingantennas. When the base station uses the single transmitting antenna, areference signal for a single antenna port is arrayed. When the basestation uses two transmitting antennas, reference signals for twotransmitting antenna ports are arrayed by using a time divisionmultiplexing (TDM) scheme and/or a frequency division multiplexing (FDM)scheme. That is, different time resources and/or different frequencyresources are allocated to the reference signals for two antenna portswhich are distinguished from each other.

Moreover, when the base station uses four transmitting antennas,reference signals for four transmitting antenna ports are arrayed byusing the TDM and/or FDM scheme. Channel information measured by adownlink signal receiving side (terminal) may be used to demodulate datatransmitted by using a transmission scheme such as single transmittingantenna transmission, transmission diversity, closed-loop spatialmultiplexing, open-loop spatial multiplexing, or multi-user MIMO.

In the case where the MIMO antenna is supported, when the referencesignal is transmitted from a specific antenna port, the reference signalis transmitted to the positions of specific resource elements accordingto a pattern of the reference signal and not transmitted to thepositions of the specific resource elements for another antenna port.That is, reference signals among different antennas are not duplicatedwith each other.

A rule of mapping the CRS to the resource block is defined as below.

$\begin{matrix}{{k = {{6m} + {\left( {v + v_{shift}} \right)\;{mod}\; 6}}}l = \left\{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix}m} = 0},1,\ldots\mspace{14mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \left\{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3\left( {n_{s}\;{mod}\; 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}\;{mod}\; 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}\;{mod}\; 6}} \right.}}} \right.} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In Equation 12, k and 1 represent the subcarrier index and the symbolindex, respectively and p represents the antenna port. N_(symb) ^(DL)represents the number of OFDM symbols in one downlink slot and N_(RB)^(DL) represents the number of radio resources allocated to thedownlink. ns represents a slot index and, N_(ID) ^(cell) represents acell ID. mod represents an modulo operation. The position of thereference signal varies depending on the v_(shift) value in thefrequency domain. Since v_(shift) is subordinated to the cell ID, theposition of the reference signal has various frequency shift valuesaccording to the cell.

In more detail, the position of the CRS may be shifted in the frequencydomain according to the cell in order to improve channel estimationperformance through the CRS. For example, when the reference signal ispositioned at an interval of three subcarriers, reference signals in onecell are allocated to a 3k-th subcarrier and a reference signal inanother cell is allocated to a 3k+1-th subcarrier. In terms of oneantenna port, the reference signals are arrayed at an interval of sixresource elements in the frequency domain and separated from a referencesignal allocated to another antenna port at an interval of threeresource elements.

In the time domain, the reference signals are arrayed at a constantinterval from symbol index 0 of each slot. The time interval is defineddifferently according to a cyclic shift length. In the case of thenormal cyclic shift, the reference signal is positioned at symbolindexes 0 and 4 of the slot and in the case of the extended CP, thereference signal is positioned at symbol indexes 0 and 3 of the slot. Areference signal for an antenna port having a maximum value between twoantenna ports is defined in one OFDM symbol. Therefore, in the case oftransmission of four transmitting antennas, reference signals forreference signal antenna ports 0 and 1 are positioned at symbol indexes0 and 4 (symbol indexes 0 and 3 in the case of the extended CP) andreference signals for antenna ports 2 and 3 are positioned at symbolindex 1 of the slot. The positions of the reference signals for antennaports 2 and 3 in the frequency domain are exchanged with each other in asecond slot.

Hereinafter, when the DRS is described in more detail, the DRS is usedfor demodulating data. A precoding weight used for a specific terminalin the MIMO antenna transmission is used without a change in order toestimate a channel associated with and corresponding to a transmissionchannel transmitted in each transmitting antenna when the terminalreceives the reference signal.

The 3GPP LTE system (for example, release-8) supports a maximum of fourtransmitting antennas and a DRS for rank 1 beamforming is defined. TheDRS for the rank 1 beamforming also means a reference signal for antennaport index 5.

A rule of mapping the DRS to the resource block is defined as below.Equation 13 shows the case of the normal CP and Equation 14 shows thecase of the extended CP.

$\begin{matrix}{{k = {{\left( k^{\prime} \right)\;{mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \left\{ {{\begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \left\{ {2,3} \right\}} \\{{4m^{\prime}} + {\left( {2 + v_{shift}} \right)\;{mod}\; 4}} & {{{if}\mspace{14mu} l} \in \left\{ {5,6} \right\}}\end{matrix}l} = \left\{ {{\begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s}\mspace{14mu}{mod}\; 2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s}\;{mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{3N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}{mod}\; 3}}} \right.} \right.} \right.}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack \\{k = {{\left( k^{\prime} \right)\;{mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}} & \left\lbrack {{Equation}\mspace{14mu} 14} \right\rbrack \\{k^{\prime} = \left\{ {{\begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {\left( {2 + v_{shift}} \right)\;{mod}\; 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix}l} = \left\{ {{\begin{matrix}4 & {l^{\prime} \in \left\{ {0,2} \right\}} \\1 & {l^{\prime} = 1}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}\mspace{11mu}{mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{4\; N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}\;{mod}\; 3}}} \right.} \right.} \right.} & \;\end{matrix}$

In Equations 12 to 14 given above, k and p represent the subcarrierindex and the antenna port, respectively. N_(RB) ^(DL), ns, and N_(ID)^(cell) represent the number of RBs, the number of slot indexes, and thenumber of cell IDs allocated to the downlink, respectively. The positionof the RS varies depending on the v_(shift) value in terms of thefrequency domain.

In Equations 13 and 14, k and 1 represent the subcarrier index and thesymbol index, respectively and p represents the antenna port. N_(sc)^(RB) represents the size of the resource block in the frequency domainand is expressed as the number of subcarriers. represents the number ofphysical resource blocks. N_(RB) ^(PDSCH) represents a frequency band ofthe resource block for the PDSCH transmission. ns represents the slotindex and N_(ID) ^(cell) represents the cell ID. mod represents themodulo operation. The position of the reference signal varies dependingon the v_(shift) value in the frequency domain. Since v_(shift) issubordinated to the cell ID, the position of the reference signal hasvarious frequency shift values according to the cell.

Sounding Reference Signal (SRS)

The SRS is primarily used for the channel quality measurement in orderto perform frequency-selective scheduling and is not associated withtransmission of the uplink data and/or control information. However, theSRS is not limited thereto and the SRS may be used for various otherpurposes for supporting improvement of power control and variousstart-up functions of terminals which have not been scheduled. Oneexample of the start-up function may include an initial modulation andcoding scheme (MCS), initial power control for data transmission, timingadvance, and frequency semi-selective scheduling. In this case, thefrequency semi-selective scheduling means scheduling that selectivelyallocates the frequency resource to the first slot of the subframe andallocates the frequency resource by pseudo-randomly hopping to anotherfrequency in the second slot.

Further, the SRS may be used for measuring the downlink channel qualityon the assumption that the radio channels between the uplink and thedownlink are reciprocal. The assumption is valid particularly in thetime division duplex in which the uplink and the downlink share the samefrequency spectrum and are divided in the time domain.

Subframes of the SRS transmitted by any terminal in the cell may beexpressed by a cell-specific broadcasting signal. A 4-bit cell-specific‘srsSubframeConfiguration’ parameter represents 15 available subframearrays in which the SRS may be transmitted through each radio frame. Bythe arrays, flexibility for adjustment of the SRS overhead is providedaccording to a deployment scenario.

A 16-th array among them completely turns off a switch of the SRS in thecell and is suitable primarily for a serving cell that serves high-speedterminals.

FIG. 16 illustrates an uplink subframe including a sounding referencesignal symbol in the wireless communication system to which the presentinvention can be applied.

Referring to FIG. 16, the SRS is continuously transmitted through a lastSC FDMA symbol on the arrayed subframes. Therefore, the SRS and the DMRSare positioned at different SC-FDMA symbols.

The PUSCH data transmission is not permitted in a specific SC-FDMAsymbol for the SRS transmission and consequently, when sounding overheadis highest, that is, even when the SRS symbol is included in allsubframes, the sounding overhead does not exceed approximately 7%.

Each SRS symbol is generated by a base sequence (random sequence or asequence set based on Zadoff-Ch (ZC)) associated with a given time wiseand a given frequency band and all terminals in the same cell use thesame base sequence. In this case, SRS transmissions from a plurality ofterminals in the same cell in the same frequency band and at the sametime are orthogonal to each other by different cyclic shifts of the basesequence to be distinguished from each other.

SRS sequences from different cells may be distinguished from each otherby allocating different base sequences to respective cells, butorthogonality among different base sequences is not assured.

Coordinated Multi-Point Transmission and Reception (COMP)

According to a demand of LTE-advanced, CoMP transmission is proposed inorder to improve the performance of the system. The CoMP is also calledco-MIMO, collaborative MIMO, network MIMO, and the like. It isanticipated that the CoMP will improves the performance of the terminalpositioned at a cell edge and improve an average throughput of the cell(sector).

In general, inter-cell interference decreases the performance and theaverage cell (sector) efficiency of the terminal positioned at the celledge in a multi-cell environment in which a frequency reuse index is 1.In order to alleviate the inter-cell interference, the LTE system adoptsa simple passive method such as fractional frequency reuse (FFR) in theLTE system so that the terminal positioned at the cell edge hasappropriate performance efficiency in an interference-limitedenvironment. However, a method that reuses the inter-cell interferenceor alleviates the inter-cell interference as a signal (desired signal)which the terminal needs to receive is more preferable instead ofreduction of the use of the frequency resource for each cell. The CoMPtransmission scheme may be adopted in order to achieve theaforementioned object.

The CoMP scheme which may be applied to the downlink may be classifiedinto a joint processing (JP) scheme and a coordinatedscheduling/beamforming (CS/CB) scheme.

In the JP scheme, the data may be used at each point (base station) in aCoMP wise. The CoMP wise means a set of base stations used in the CoMPscheme. The JP scheme may be again classified into a joint transmissionscheme and a dynamic cell selection scheme.

The joint transmission scheme means a scheme in which the signal issimultaneously transmitted through a plurality of points which are allor fractional points in the CoMP wise. That is, data transmitted to asingle terminal may be simultaneously transmitted from a plurality oftransmission points. Through the joint transmission scheme, the qualityof the signal transmitted to the terminal may be improved regardless ofcoherently or non-coherently and interference with another terminal maybe actively removed.

The dynamic cell selection scheme means a scheme in which the signal istransmitted from the single point through the PDSCH in the CoMP wise.That is, data transmitted to the single terminal at a specific time istransmitted from the single point and data is not transmitted to theterminal at another point in the CoMP wise. The point that transmits thedata to the terminal may be dynamically selected.

According to the CS/CB scheme, the CoMP wise performs beamformingthrough coordination for transmitting the data to the single terminal.That is, the data is transmitted to the terminal only in the servingcell, but user scheduling/beamforming may be determined throughcoordination of a plurality of cells in the CoMP wise.

In the case of the uplink, CoMP reception means receiving the signaltransmitted by the coordination among a plurality of points which aregeographically separated. The CoMP scheme which may be applied to theuplink may be classified into a joint reception (JR) scheme and thecoordinated scheduling/beamforming (CS/CB) scheme.

The JR scheme means a scheme in which the plurality of points which areall or fractional points receives the signal transmitted through thePDSCH in the CoMP wise. In the CS/CB scheme, only the single pointreceives the signal transmitted through the PDSCH, but the userscheduling/beamforming may be determined through the coordination of theplurality of cells in the CoMP wise.

Relay Node (RN)

The relay node transfers data transmitted and received between the basestation and the terminal through two different links (a backhaul linkand an access link). The base station may include a donor cell. Therelay node is wirelessly connected to a wireless access network throughthe donor cell.

Meanwhile, in respect to the use of a band (spectrum) of the relay node,a case in which the backhaul link operates in the same frequency band asthe access link is referred to as ‘in-band’ and a case in which thebackhaul link and the access link operate in different frequency bandsis referred to as ‘out-band’. In both the cases of the in-band and theout-band, a terminal (hereinafter, referred to as a legacy terminal)that operates according to the existing LTE system (for example,release-8) needs to be able to access the donor cell.

The relay node may be classified into a transparent relay node or anon-transparent relay node according to whether the terminal recognizingthe relay node. Transparent means a case in which it may not berecognized whether the terminal communicates with the network throughthe relay node and non-transparent means a case in which it isrecognized whether the terminal communicates with the network throughthe relay node.

In respect to control of the relay node, the relay node may be dividedinto a relay node which is constituted as a part of the donor cell or arelay node that autonomously controls the cell.

The relay node which is constituted as a part of the donor cell may havea relay node identity (ID), but does not have a cell identity thereof.

When at least a part of radio resource management (RRM) is controlled bya base station to which the donor cell belongs, even though residualparts of the RRM are positioned at the relay node, the relay node isreferred to as the relay node which is constituted as a part of thedonor cell. Preferably, the relay node may support the legacy terminal.For example, various types including smart repeaters, decode-and-forwardrelay nodes, L2 (second layer) relay nodes, and the like and a type-2relay node correspond to the relay node.

In the case of the relay node that autonomously controls the cell, therelay node controls one or a plurality of cells and unique physicallayer cell identities are provided to the respective cells controlled bythe relay node. Further, the respective cells controlled by the relaynode may use the same RRM mechanism. In terms of the terminal, there isno difference between accessing the cell controlled by the relay nodeand accessing a cell controlled by a general base station. The cellcontrolled by the relay node may support the legacy terminal. Forexample, a self-backhauling relay node, an L3 (third layer) relay node,a type-1 relay node, and a type-1a relay node correspond to the relaynode.

The type-1 relay node as the in-band relay node controls a plurality ofcells and the plurality of respective cells are recognized as separatecells distinguished from the donor cell in terms of the terminal.Further, the plurality of respective cells may have physical cell IDs(they are defined in the LTE release-8) and the relay node may transmita synchronization channel, the reference signal, and the like thereof.In the case of a single-cell operation, the terminal may receivescheduling information and an HARQ feedback directly from the relay nodeand transmit control channels (scheduling request (SR), CQI, ACK/NACK,and the like) thereof to the relay node. Further, the type-1 relay nodeis shown as a legacy base station (a base station that operatesaccording to the LTE release-8 system) to the legacy terminals (terminalthat operate according to the LTE release-8 system). That is, the type-1relay node has the backward compatibility. Meanwhile, the terminals thatoperate according to the LTE-A system recognize the type-1 relay node asa base station different from the legacy base station to provideperformance improvement.

The type-1a relay node has the same features as the type-1 relay nodeincluding operating as the out-band. The operation of the type-1a relaynode may be configured so that an influence on an L1 (first layer)operation is minimized or is not present.

The type-2 relay node as the in-band relay node does not have a separatephysical cell ID, and as a result, a new cell is not formed. The type-2relay node is transparent with respect to the legacy terminal and thelegacy terminal may not recognize the presence of the type-2 relay node.The type-2 relay node may transmit the PDSCH, but at least does nottransmit the CRS and the PDCCH.

Meanwhile, in order for the relay node to operate as the in-band, someresources in the time-frequency space needs to be reserved for thebackhaul link and the resources may be configured not to be used for theaccess link. This is referred to as resource partitioning.

A general principle in the resource partitioning in the relay node maybe described as below. Backhaul downlink and access downlink may bemultiplexed in the time division multiplexing scheme on one carrierfrequency (that is, only one of the backhaul downlink and the accessdownlink is activated at a specific time). Similarly, backhaul uplinkand access uplink may be multiplexed in the time division multiplexingscheme on one carrier frequency (that is, only one of the backhauluplink and the access uplink is activated at a specific time).

In the backhaul link multiplexing in the FDD, backhaul downlinktransmission may be performed in a downlink frequency band and backhauluplink transmission may be performed in an uplink frequency band. In thebackhaul link multiplexing in the TDD, THE backhaul downlinktransmission may be performed in the downlink subframe of the basestation and the relay node and the backhaul uplink transmission may beperformed in the uplink subframe of the base station and the relay node.

In the case of the in-band relay node, for example, when both backhauldownlink reception from the base station and access downlinktransmission to the terminal are performed in the same frequency band,signal interference may occurs at a receiver side of the relay node by asignal transmitted from a transmitter side of the relay node. That is,the signal interference or RF jamming may occur at an RF front-end ofthe relay node. Similarly, even when both the backhaul uplinktransmission to the base station and the access uplink reception fromthe terminal are performed in the same frequency band, the signalinterference may occur.

Therefore, in order for the relay node to simultaneously transmit andreceive the signal in the same frequency band, when sufficientseparation (for example, the transmitting antenna and the receivingantenna are installed to be significantly geographically spaced apartfrom each other like installation on the ground and underground) betweena received signal and a transmitted signal is not provided, it isdifficult to implement the transmission and reception of the signal.

As one scheme for solving a problem of the signal interference, therelay node operates not transmit the signal to the terminal whilereceiving the signal from the donor cell. That is, a gap is generated intransmission from the relay node to the terminal and the terminal may beconfigured not to expect any transmission from the relay node during thegap. The gap may be configured to constitute a multicast broadcastsingle frequency network (MBSFN) subframe.

FIG. 17 illustrates a structure of relay resource partitioning in thewireless communication system to which the present invention can beapplied.

In FIG. 17, in the case of a first subframe as a general subframe, adownlink (that is, access downlink) control signal and downlink data aretransmitted from the relay node and in the case of a second subframe asthe MBSFN subframe, the control signal is transmitted from the relaynode from the terminal in the control region of the downlink subframe,but no transmission is performed from the relay node to the terminal inresidual regions. Herein, since the legacy terminal expects transmissionof the PDCCH in all downlink subframes (in other words, since the relaynode needs to support legacy terminals in a region thereof to perform ameasurement function by receiving the PDCCH every subframe), the PDCCHneeds to be transmitted in all downlink subframes for a correctoperation of the legacy terminal. Therefore, eve on a subframe (secondsubframe) configured for downlink (that is, backhaul downlink)transmission from the base station to the relay node, the relay does notreceive the backhaul downlink but needs to perform the access downlinktransmission in first N (N=1, 2, or 3) OFDM symbol intervals of thesubframe. In this regard, since the PDCCH is transmitted from the relaynode to the terminal in the control region of the second subframe, thebackward compatibility to the legacy terminal, which is served by therelay node may be provided. In residual regions of the second subframe,the relay node may receive transmission from the base station while notransmission is performed from the relay node to the terminal.Therefore, through the resource partitioning scheme, the access downlinktransmission and the backhaul downlink reception may not besimultaneously performed in the in-band relay node.

The second subframe using the MBSFN subframe will be described indetail. The control region of the second subframe may be referred to asa relay non-hearing interval. The relay non-hearing interval means aninterval in which the relay node does not receive the backhaul downlinksignal and transmits the access downlink signal. The interval may beconfigured by the OFDM length of 1, 2, or 3 as described above. In therelay node non-hearing interval, the relay node may perform the accessdownlink transmission to the terminal and in the residual regions, therelay node may receive the backhaul downlink from the base station. Inthis case, since the relay node may not simultaneously performtransmission and reception in the same frequency band, It takes a timefor the relay node to switch from a transmission mode to a receptionmode. Therefore, in a first partial interval of a backhaul downlinkreceiving region, a guard time (GT) needs to be set so that the relaynode switches to the transmission/reception mode. Similarly, even whenthe relay node operates to receive the backhaul downlink from the basestation and transmit the access downlink to the terminal, the guard timefor the reception/transmission mode switching of the relay node may beset. The length of the guard time may be given as a value of the timedomain and for example, given as a value of k (k≥1) time samples (Ts) orset to the length of one or more OFDM symbols. Alternatively, when therelay node backhaul downlink subframes are consecutively configured oraccording to a predetermines subframe timing alignment relationship, aguard time of a last part of the subframe may not be defined or set. Theguard time may be defined only in the frequency domain configured forthe backhaul downlink subframe transmission in order to maintain thebackward compatibility (when the guard time is set in the accessdownlink interval, the legacy terminal may not be supported). In thebackhaul downlink reception interval other than the guard time, therelay node may receive the PDCCH and the PDSCH from the base station.This may be expressed as a relay (R)-PDCCH and a relay-PDSCH (R-PDSCH)in a meaning of a relay node dedicated physical channel.

Channel State Information (CSI) Feed-Back

The MIMO scheme may be divided into an open-loop scheme and aclosed-loop scheme. The open-loop MIMO scheme means that the transmitterside performs MIMO transmission without a feed-back of the channel stateinformation from the MIMO receiver side. The closed-loop MIMO schememeans that the transmitter side performs the MIMO transmission byreceiving the feed-back of the channel state information from the MIMOreceiver side. In the closed-loop MIMO scheme, each of the transmitterside and the receiver side may perform the beamforming based on thechannel state information in order to acquire a multiplexing gain of theMIMO transmitting antenna. The transmitter side (for example, the basestation) may allocate an uplink control channel or an uplink sharechannel to the receiver side (for example, the terminal).

The channel state information (CSI) which is fed back may include therank indicator (RI), the precoding matrix index (PMI), and the channelquality indicator (CQI).

The RI is information on the rank of the channel. The rank of thechannel means the maximum number of layers (alternatively, streams)which may send different information through the same time-frequencyresource. Since a rank value is primary determined by long-time fadingof the channel, the RI may be generally fed back according to a longerperiod (that is, less frequently) than the PMI and the CQI.

The PMI is information on the precoding matrix used for transmissionfrom the transmitter side and a value acquired by reflecting spatialcharacteristics of the channel. Precoding means mapping the transmissionlayer to the transmitting antenna and a layer-antenna mappingrelationship may be determined by a precoding matrix. The PMIcorresponds to a precoding matrix index of the base station, which theterminal prefers to based on a measurement value (metric) such as asignal-to-interference plus noise ratio (SINR), or the like. In order toreduce feed-back overhead of precoding information, a scheme may beused, in which the transmitter side and the receiver side previouslyshare a codebook including various precoding matrices and feed back onlyan index indicating a specific precoding matrix.

The CQI is information indicating the channel quality or a channelintensity. The CQI may be expressed as a predetermined MCS combination.That is, the CQI which is fed back indicates a corresponding modulationscheme and a corresponding code rate. In general, the CQI becomes avalue acquired by reflecting a received SINR which may be acquired whenthe base station configures a spatial channel by using the PMI.

In the system (for example, LTE-A system) supporting the extendedantenna configuration, acquiring additional multi-user diversity byusing a multi-user-MIMO (MU-MIMO) scheme is considered. In the MU-MIMOscheme, since an interference channel between terminals multiplexed inan antenna domain is present, when the base station performs downlinktransmission by using the channel state information which one terminalamong the multi users feeds back, the interference in another terminalneeds to be prevented. Therefore, channel state information havinghigher accuracy needs to be fed back than a single-user-MIMO (SU-MIMO)scheme in order to correctly perform the MU-MIMO operation.

A new CSI feed-back scheme that enhances the CSI constituted by the RI,the PMI, and the CQI may be adopted in order to measure and report themore accurate channel state information. For example, the precodinginformation which the receiver side feeds back may be indicated bycombining two PMIs. One (first PMI) among two PMIs may have an attributeof a long term and/or a wideband and be designated as W1. The other one(second PMI) among two PMIs may have an attribute of a short term and/ora subband and be designated as W2. A final PMI may be determined by acombination (alternatively, function) of W1 and W2. For example, whenthe final PMI is referred to as W, W may be defined as W=W1*W2 orW=W2*W1.

Herein, W1 reflects average frequency and/or temporal characteristics ofthe channel. In other words, W may be defined as the channel stateinformation reflecting a characteristic of a long term channel on thetime, reflecting a characteristic of a wideband channel on thefrequency, or reflecting the characteristics of the long term channel onthe time and the wideband channel on the frequency. In order to expressthe characteristics of W1 in brief, W1 is referred to as the channelstate information (alternatively, long term-wideband PMI) of the longterm and wideband attributes.

Meanwhile, W2 reflects a relatively more instantaneous channelcharacteristic than W1. In other words, W2 may be defined as the channelstate information reflecting a characteristic of a short-term channel onthe time, reflecting a characteristic of a subband channel on thefrequency, or reflecting the characteristics of the short term channelon the time and the subband channel on the frequency. In order toexpress the characteristics of W2 in brief, W2 is referred to as thechannel state information (alternatively, short term-subband PMI) of theshort term and subband attributes.

In order to determine one final precoding matrix W from the information(for example, W1 and W2) of two different attributes indicating thechannel state, separate codebooks (that is, a first codebook for W1 anda second codebook for W2) constituted by the precoding matrixesindicating the channel information of the respective attributes need tobe configured. A type of the codebook configured as above may bereferred to as a hierarchical codebook. Further, determining a codebookto be finally used by using the hierarchical codebook may be referred toas hierarchical codebook transformation.

In the case of using the code book, higher-accuracy channel feed-back ispossible than in the case of using a single codebook. Single-cellMU-MIMO and/or multi-cell coordinated communication may be supported byusing the high-accuracy channel feed-back.

Enhanced PMI for MU-MIMO or CoMP

In a next-generation communication standard such as LTE-A, in order toachieve high transmission rate, transmission schemes such as MU-MIMO andCoMP were proposed. In order to implement the improved transmissionschemes, the UE needs to feedback complicated and various CSIs to thebase station.

For example, in the MU-MIMO, when UE-A selects the PMI, a CSI feedbackscheme which uploads desired PMI of the UE-A and the PMI (hereinafter,referred to as best companion PMI (BCPMI)) of the UE scheduled with theUE-A.

That is, in the precoding matrix codebook, when co-scheduled UE is usedas a precoder, the BCPMI which gives less interference to the UE-A iscalculated and additionally fed-back to the base station.

The base station MU-MIMO-schedules another UE preferring UE-A and bestcompanion precoding matrix (BCPM) (precoding matrix corresponding to theBCPMI) precoding by using the information.

The BCPMI feedback scheme is divided into two of an explicit feedbackand an implicit feedback according to presence and absence of thefeedback payload.

First, there is the explicit feedback scheme with the feedback payload.

In the explicit feedback scheme, the UE-A determines the BCPMI in theprecoding matrix codebook and then feedbacks the determined BCPMI to thebase station through a control channel. As one scheme, the UE-A selectsan interference signal precoding matrix in which estimated SINR ismaximized in the codebook and feedbacks the selected interference signalprecoding matrix as the BCPMI value.

As an advantage of the explicit feedback, the BCPMI with more effectiveinterference removal may be selected and transmitted. The UE determinesthe most effective value in the interference removal as the BCPMI byassuming all the codewords in the codebook one by one as theinterference beam and comparing the metric such as SINR. However, as thecodebook size is increased, the candidates of the BCPMI are increased,and thus the larger feedback payload size is required.

Second, there is the explicit feedback scheme without the feedbackpayload.

The implicit feedback scheme is a scheme that the UE-A does not search acodeword which receives less interference in the codebook to select thesearched codeword as the BCPMI, but statically determines the BCPMIcorresponding to the desired PMI when the desired PMI is determined. Inthis case, it may be preferred that the BCPM is constituted byorthogonal vectors in the determined desired PMI.

The reason is that the desired PM is set in a direction to maximize thechannel gain of the channel H in order to maximize the received SINR andthus, it is effective in mitigating the interference the interferencesignal is selected by avoiding in the direction of the PM. When thechannel H is analyzed as the plurality of independent channels throughthe singular value decomposition (SVD), the BCPMI determination schemeis further justified. 4×4 channel H may be decomposed through the SVDlike the following Equation 15.

$\begin{matrix}{H = {{ULV}^{H} = {{\begin{bmatrix}u_{1} & u_{2} & u_{3} & u_{4}\end{bmatrix}\begin{bmatrix}\lambda_{1} & 0 & 0 & 0 \\0 & \lambda_{2} & 0 & 0 \\0 & 0 & \lambda_{3} & 0 \\0 & 0 & 0 & \lambda_{4}\end{bmatrix}}\begin{bmatrix}v_{1}^{H} \\v_{2}^{H} \\v_{3}^{H} \\v_{4}^{H}\end{bmatrix}}}} & \left\lbrack {{Equation}\mspace{14mu} 15} \right\rbrack\end{matrix}$

In Equation 15, U, V are unitary matrices, ui, vi, and λ_(i) represent a4×1 left singular vector, a 4×1 right singular vector, and a singularvalue of the channel H, respectively and arranged in descending order ofλ_(i)>λ_(i+1). In the case of using the beamforming matrix V in thetransmission terminal and the beamforming matrix U^(H) in the receptionterminal, all channel gains which may be theoretically obtained may beobtained without loss.

In the case of Rank 1, using the transmission beamforming vector v1 andthe reception beamforming vector u1 may obtain the channel |λ₁|² to gainobtain optimal performance in terms of the SNR. For example, it isadvantageous that the UE-A selects the most similar PM to v1 in the caseof rank 1. Ideally, when the desired PM completely coincides with v1,the reception beam is set to u1 and the transmission beam of theinterference signal is set to the PM in the orthogonal direction tocompletely remove the interference signal without loss in the desiredsignal. Actually, due to the quantization error, when the desired PM hasa slight difference from v1, the transmission beam of the interferencesignal set in the orthogonal direction to the PM is no longer equal tothe orthogonal beam to v1, and thus, the desired signal may notcompletely remove the interference signal without loss of the desiredsignal, but when the quantization error is small to help in controllingthe interference signal.

As an example of the implicit feedback, in the case of using the LTEcodebook, the BCPMI may be statically determined as the vector indexorthogonal to the PMI.

It is assumed that the transmission antennas are four and the receptionrank of the UE feedbacking the PMI is 1, three vectors orthogonal to thedesired PMI are expressed as three BCPMIs.

For example, in the case of PMI=3, BCPMI=0, 1, 2. The PMI and the BCPMIrepresent the index of the 4×1 vector codeword in the codebook. The basestation uses some or all as the precoder of the co-schedule UE byconsidering the BCPMI set(BCPMI=0, 1, 2) as the effective precodingindex in the interference removal.

The implicit PMI has an advantage in that there is no additionalfeedback overhead because the desired PMI and the BCPMI set are mappedto 1:1. However, due to the quantization error of the desired PM (PM:precoding matrix corresponding to the PMI), the BCPM subordinatedthereto may have optimal beam direction and error for the interferenceremoval. When there is no quantization error, three BCPMs representinterference beam (ideal interference beam) which completely removes allthe interference, but when there is the error, each BCPM occurs adifference from the ideal interference beam.

Further, the difference from the ideal interference beam of each BCPM isaveragely the same, but may be different at a certain moment. Forexample, when desired PMI=3, it may be effective in removing theinterference signal in order of BCPMI 0, 1, and 2, and the base stationwhich does not know a relative error of BCPMI 0, 1, and 2 maycommunicate while the strong interference between the co-scheduled UEsis present by determining BCPMI 2 with the largest error with the idealinterference beam as the beam of the interference signal.

Cross-CC Scheduling and E-PDCCH Scheduling

Next, cross-CC scheduling and E-PDCCH scheduling will be describedbriefly.

Regarding definitions of cross-CC scheduling operation in an aggregationcontext of a plurality of CC (Component Carrier=(serving) cell) in anexisting 3GPP LTE Rel-10 system, one CC (i.e. scheduled CC) may bepreset to receive DL/UL scheduling from the specific one CC (i.e.scheduling CC) (i.e., to receive DL/UL grant PDCCH for an associatedscheduled CC, and the associated scheduling CC may basically performDL/UL scheduling therefor.

In other words, all of SSs for PDCCH a scheduling scheduling/scheduledCC in a relationship with the cross-CC scheduling may be present in acontrol channel region of the scheduling CC.

On the other hand, as for FDD DL carrier or TDD DL subframes in a LTEsystem, first n OFDM symbols thereof may be used to transmit PDCCH,PHICH, PCFICH, etc. as physical channels for transmission of variouscontrol indicator transmissions, and remaining OFDM symbols thereof maybe used for PDSCH transmission.

In this connection, a number of symbols used for control channeltransmission in each subframe may be transferred to a device over aphysical channel including PCFICH, etc. dynamically or in a semi-staticmanner via RRC signaling.

In this connection, specifically, a n value may be set, at most, to from1 to 4 symbols based on a subframe characteristic and systemcharacteristic (FDD/TDD, system bandwidth, etc.).

On the other hand, in an existing LTE system, since it has a limitationthat PDCCH as a physical channel for transmission of various controlinformation and DL/UL scheduling is transmitted via limited OFDMsymbols, instead of a control channel transmitted via an OFDM symbolseparated from a PDSCH such as PDCCH, enhanced PDCCH (i.e. E-PDCCH)being multiplexed more freely in a PDSCH and FDM/TDM manner may beintroduced.

Quasi Co-Location

Next, a Quasi co-location will be descried briefly.

Hereinafter, a term “quasi co-located (QC)” (or “quasi co-location(QC)”) may be defined as follows:

“If two antenna ports are “quasi co-located (QC)”, the UE may assumethat large-scale properties of the signal received from the firstantenna port can be inferred from the signal received from the otherantenna port”. The “large-scale properties” mentioned in the abovedefinition consist of some or all of;

-   -   Delay spread    -   Doppler spread    -   Frequency shift    -   Average received power    -   Received Timing

In an alternative, the definition may be re-expressed in a variantthereof in terms of a channel:

“If two antenna ports are “quasi co-located (QC)”, the UE may assumethat large-scale properties of the channel over which a symbol on oneantenna port is conveyed can be inferred from the channel over which asymbol on the other antenna port is conveyed”. The “large-scaleproperties” mentioned in the above definition consist of some or all of:

-   -   Delay spread    -   Doppler spread    -   Doppler shift    -   Average gain    -   Average delay

As used herein, the above QC related definitions will be usedinterchangeably.

That is, the QC concept may follow any one of the above definitions. Inan alternative, a QC definition may be as follows:

between antenna ports complying with the QC assumption, it seems likethat transmissions occur from a co-location (e.g., the UE may assumethat the antenna ports are those transmitting from the same transmissionpoint).

By the above definition, the UE may not assume the same large-scalechannel properties between associated antenna ports (APs) for“non-quasi-co-located (NQC) antenna ports”.

That is, in this case, a conventional UE receiver should preformindividual processing between non-quasi-co-located(NQC) APs set fortiming acquisition and tracking, frequency offset estimation andcompensation, delay estimation, and Doppler estimation, etc.respectively. For between the Aps assuming the QC, the UE mayadvantageously perform following operations:

For Delay spread & Doppler spread, UE may apply equally estimations ofpower-delay-profile, delay spread and Doppler spectrum, Doppler spreadfor one certain port to Wiener filter, etc. used for channel estimationfor another port.

For Frequency shift & Received Timing, UE may perform time and frequencysynchronization for one certain port, and may apply the samesynchronization to decoding of another port.

For an average received power, the UE may perform averaging of RSRPmeasurements over two or more antenna ports.

HARQ Procedure

In a mobile communication system, for one cell/sector, one base stationmay communicate data with multiple devices over a wireless channelenvironment. In a multi-carrier wave system or in a system operating ina similar form thereto, the base station may receive a packet trafficfrom wired Internet and may send the packet traffic to each device usinga given communication protocol.

In this connection, the base station determining a device to receivedownlink data, and a frequency region and timing for transmission of thedownlink data may refer to a downlink scheduling.

Further, the base station may receive and decode data from the deviceusing a given communication protocol and then send a packet traffic tothe wired Internet. In this connection, the base station determining adevice to transmit uplink data thereto, and a frequency region andtiming for the transmission may refer to an uplink scheduling.

Generally, a device with a better channel state may communicate data formore timing using more frequency resources.

In a multi-carrier wave system or in a system operating in a similarform thereto, a resource may be mainly divided into time and frequencyregions. The resource may be again defined into a resource block, wherethe block may be formed of any N number of sub-carrier waves and any Mnumber of sub-frames or given time units. In this connection, each of Nand M may be 1.

A single resource block may have one axis as multiple sub-carrier wavesand the other axis as a given time unit.

For the downlink, the base station may schedule one or more resourceblock toward a device selected based on a given scheduling rule, and maytransmit data to the device using an allocated resource block.

For the uplink, the base station may schedule one or more resource blocktoward a device selected based on a given scheduling rule, and thedevice may transmit uplink data using an allocated resource.

A method for controlling an error when a frame is lost or damaged afterscheduling and then data transmission may include an ARQ (AutomaticRepeat request) approach and HARQ (hybrid ARQ) approach, wherein thelatter is more improved than the former.

Basically, in the ARQ scheme, after transmission of a single frame, atransmission side may wait for a confirmation message (ACK); only when areceipt side successfully receives the frame, the receipt side may sendthe confirmation message (ACK). Otherwise, when the frame has an error,the receipt side may send a NACK(negative-ACK) message, and may deleteinformation thereof from a receipt state buffer for the frame with theerror.

When the transmission side receives the ACK signal, the transmissionside will send a subsequent frame. However, when receiving the NACKmessage, the transmission side will re-transmit the frame. Unlike theARQ scheme, in the HARQ scheme, when being unable to decode the receivedframe, the receipt stage may send the NACK message to the transmissionstage. However, an already-received frame may be stored in a buffer fora given duration, and may be combined with a re-transmitted frame toimprove a receipt success rate.

Recently, rather than a basic ARQ scheme, a more efficient HARQ schemehas been widely employed. Such a HARQ scheme may be divided intosynchronous HARQ and asynchronous HARQ schemes based on re-transmissiontiming, and into channel-adaptive and channel-non-adaptive schemes basedon whether to reflect a channel state relative to an amount of aresource used in re-transmission.

In the synchronous HARQ scheme, when an initial transmission fails, asubsequent re-transmission may be carried out by the system at a giventiming. That is, with assumption that a re-transmission timing occursevery fourth time unit after the initial transmission fails, the timingneeds not be additionally informed because there is already establishedan agreement between the base station and device in terms of the timing.

However, when a transmission side has received the NACK message, it mayperform frame re-transmission every fourth time unit until receiving theACK message.

To the contrary, in the Asynchronous HARQ scheme, the re-transmissiontiming may be newly scheduled or may be achieved via an additionalsignaling. A re-transmission timing for the frame which failed to bereceived successfully may vary due to various factors including achannel state, etc.

In the Channel-non-adaptive HARQ scheme, frame modulation or a number ofresource blocks used, AMC, etc. in a re-transmission may be set as it isin an initial transmission. Otherwise, in the channel-adaptive HARQscheme, the frame modulation or a number of resource blocks used, AMC,etc. in a re-transmission may vary based on a channel state.

For example, in the channel-non-adaptive scheme, when the transmissionside sends data using six resource blocks in the initial transmission,the transmission side re-sends data using six resource blocks in there-transmission.

To the contrary, in the channel-adaptive scheme, when the transmissionside sends data using six resource blocks in the initial transmission,the transmission side re-sends data using larger or smaller than 6resource blocks in the re-transmission based on the channel state.

Thus, based on the above classification, four combinations of HARQs maybe achieved. However, mainly employed HARQ schemes may be theasynchronous and channel-adaptive HARQ scheme and synchronous andchannel-non-adaptive HARQ scheme.

The asynchronous and channel-adaptive HARQ scheme may have a benefitthat the re-transmission timing and the resource amount used mayadaptively vary based on the channel state, thereby to maximize there-transmission efficiency, but may have a shortcoming that an overhandmay increase. Thus, this scheme may not be generally considered for anuplink direction.

On the other hand, the synchronous and channel-non-adaptive HARQ schememay have a benefit that the re-transmission timing and resourceassignment may be predetermined in the system, thereby to substantiallyremove the overhead, but may have a shortcoming that a re-transmissionefficiency may be very low when the channel state has remarkablefluctuations. Currently, for a downlink in a 3GPP LTE, the asynchronousHARQ scheme has been employed, while for an uplink in a 3GPP LTE, thesynchronous HARQ scheme has been employed.

On the other hand, for example, for the downlink, after the schedulingand data transmission, there may be a delay between a time when ACK/NAKinformation is received from the device and a time when next datatransmission occurs.

This may be due to a channel propagation delay and a time taken for datadecoding and data encoding. For data transmission without blank durationdue to this delay, an independent HARQ process may be used fortransmission.

For example, when a shortest period between current data transmissionand next data transmission is 7 subframes, 7 independent processes maybe intervened therebetween, to allow the data transmission without blankduration due to the delay. In LTE, when not operating in MIMO, at most 8processes may be allocated.

General D2D Communication

Generally, D2D communication is limitatively used as the term forcommunication between objects or object intelligent communication, butthe D2D communication in the present invention may include allcommunication between various types of devices having a communicationfunction such as a smart phone and a personal computer in addition tosimple devices with a communication function.

FIG. 18 is a diagram for schematically describing the D2D communicationin a wireless communication system to which the present invention may beapplied.

FIG. 18A illustrates a communication scheme based on an existing basestation eNB, and the UE1 may transmit the data to the base station onthe uplink and the base station may transmit the data to the UE2 on thedownlink. The communication scheme may be referred to as an indirectcommunication scheme through the base station. In the indirectcommunication scheme, a Un link (referred to as a backhole link as alink between base stations or a link between the base station and therepeater) and/or a Uu link (referred to as an access link as a linkbetween the base station and the UE or a link between the repeater andthe UE) which are defined in the existing wireless communication systemmay be related.

FIG. 18B illustrates a UE-to-UE communication scheme as an example ofthe D2D communication, and the data exchange between the UEs may beperformed without passing through the base station. The communicationscheme may be referred to as a direct communication scheme betweendevices. The D2D direct communication scheme has advantages of reducinglatency and using smaller wireless resources as compared with theexisting indirect communication scheme through the base station.

FIG. 19 illustrates examples of various scenarios of the D2Dcommunication to which the method proposed in the specification may beapplied.

The D2D communication scenario may be divided into (1) anout-of-coverage network, (2) a partial-coverage network, and (3)in-coverage network according to whether the UE1 and the UE2 arepositioned in coverage/out-of-coverage.

The in-coverage network may be divided into an in-coverage-single-celland an in-coverage-multi-cell according to the number of cellscorresponding to the coverage of the base station.

FIG. 19a illustrates an example of an out-of-coverage network scenarioof the D2D communication.

The out-of-coverage network scenario means perform the D2D communicationbetween the D2D UEs without control of the base station.

In FIG. 19a , only the UE1 and the UE2 are present and the UE1 and theUE2 may directly communicate with each other.

FIG. 19b illustrates an example of a partial-coverage network scenarioof the D2D communication.

The partial-coverage network scenario means performing the D2Dcommunication between the D2D UE positioned in the network coverage andthe D2D UE positioned out of the network coverage.

In FIG. 19b , it may be illustrated that the D2D UE positioned in thenetwork coverage and the D2D UE positioned out of the network coveragecommunicate with each other.

FIG. 19c illustrates an example of the in-coverage-single-cell and FIG.19d illustrates an example of the in-coverage-multi-cell scenario.

The in-coverage network scenario means that the D2D UEs perform the D2Dcommunication through the control of the base station in the networkcoverage.

In FIG. 19c , the UE1 and the UE2 are positioned in the same networkcoverage (alternatively, cell) under the control of the base station.

In FIG. 19d , the UE1 and the UE2 are positioned in the networkcoverage, but positioned in different network coverages. In addition,the UE1 and the UE2 performs the D2D communication under the control ofthe base station managing the network coverage.

Here, the D2D communication will be described in more detail.

The D2D communication may operate in the scenario illustrated in FIG.19, but generally operate in the network coverage and out of the networkcoverage. The link used for the D2D communication (direct communicationbetween the UEs) may be referred to as D2D link, directlink, orsidelink, but for the convenience of description, the link is commonlyreferred to as the sidelink.

The sidelink transmission may operate in uplink spectrum in the case ofthe FDD and in the uplink (alternatively, downlink) subframe in the caseof the TDD. For multiplexing the sidelink transmission and the uplinktransmission, time division multiplexing (TDM) may be used.

The sidelink transmission and the uplink transmission do notsimultaneously occur. In the uplink subframe used for the uplinktransmission and the sidelink subframe which partially or entirelyoverlaps with UpPTS, the sidelink transmission does not occur.Alternatively, the transmission and the reception of the sidelink do notsimultaneously occur.

A structure of a physical resource used in the sidelink transmission maybe used equally to the structure of the uplink physical resource.However, the last symbol of the sidelink subframe is constituted by aguard period and not used in the sidelink transmission.

The sidelink subframe may be constituted by extended CP or normal CP.

The D2D communication may be largely divided into discovery, directcommunication, and synchronization.

1) Discovery

The D2D discovery may be applied in the network coverage. (includinginter-cell and intra-cell). Displacement of synchronous or asynchronouscells may be considered in the inter-cell coverage. The D2D discoverymay be used for various commercial purposes such as advertisement,coupon issue, and finding friends to the UE in the near area.

When the UE 1 has a role of the discovery message transmission, the UE 1transmits the discovery message and the UE 2 receives the discoverymessage. The transmission and the reception of the UE 1 and the UE 2 maybe reversed. The transmission from the UE 1 may be received by one ormore UEs such as UE2.

The discovery message may include a single MAC PDU, and here, the singleMAC PDU may include a UE ID and an application ID.

A physical sidelink discovery channel (PSDCH) may be defined as thechannel transmitting the discovery message. The structure of the PSDCHchannel may reuse the PUSCH structure.

A method of allocating resources for the D2D discovery may use two typesType 1 and Type 2.

In Type 1, eNB may allocate resources for transmitting the discoverymessage by a non-UE specific method.

In detail, a wireless resource pool for discovery transmission andreception constituted by the plurality of subframes is allocated at apredetermined period, and the discovery transmission UE transmits thenext discovery message which randomly selects the specific resource inthe wireless resource pool.

The periodical discovery resource pool may be allocated for thediscovery signal transmission by a semi-static method. Settinginformation of the discovery resource pool for the discoverytransmission includes a discovery period, the number of subframes whichmay be used for transmission of the discovery signal in the discoveryperiod (that is, the number of subframes constituted by the wirelessresource pool).

In the case of the in-coverage UE, the discovery resource pool for thediscovery transmission is set by the eNB and may notified to the UE byusing RRC signaling (for example, a system information block (SIB)).

The discovery resource pool allocated for the discovery in one discoveryperiod may be multiplexed to TDM and/or FDM as a time-frequency resourceblock with the same size, and the time-frequency resource block with thesame size may be referred to as a ‘discovery resource’.

The discovery resource may be used for transmitting the discovery MACPDU by one UE. The transmission of the MAC PDU transmitted by one UE maybe repeated (for example, repeated four times) contiguously ornon-contiguously in the discovery period (that is, the wireless resourcepool). The UE randomly selects the first discovery resource in thediscovery resource set) which may be used for the repeated transmissionof the MAC PDU and other discovery resources may be determined inrelation with the first discovery resource. For example, a predeterminedpattern is preset and according to a position of the first selecteddiscovery resource, the next discovery resource may be determinedaccording to a predetermined pattern. Further, the UE may randomlyselect each discovery resource in the discovery resource set which maybe used for the repeated transmission of the MAC PDU.

In Type 2, the resource for the discovery message transmission isUE-specifically allocated. Type 2 is sub-divided into Type-2A andType-2B again. Type-2A is a type in which the UE allocates the resourceevery transmission instance of the discovery message in the discoveryperiod, and the type 2B is a type in which the resource is allocated bya semi-persistent method.

In the case of Type 2B, RRC_CONNECTED UE request allocation of theresource for transmission of the D2D discovery message to the eNBthrough the RRC signaling. In addition, the eNB may allocate theresource through the RRC signaling. When the UE is transited to aRRC_IDLE state or the eNB withdraws the resource allocation through theRRC signaling, the UE releases the transmission resource allocated last.As such, in the case of the type 2B, the wireless resource is allocatedby the RRC signaling and activation/deactivation of the wirelessresource allocated by the PDCCH may be determined.

The wireless resource pool for the discovery message reception is set bythe eNB and may notified to the UE by using RRC signaling (for example,a system information block (SIB)).

The discovery message reception UE monitors all of the discoveryresource pools of Type 1 and Type 2 for the discovery message reception.

2) Direct Communication

An application area of the D2D direct communication includes in-coverageand out-of-coverage, and edge-of-coverage. The D2D direct communicationmay be used on the purpose of public safety (PS) and the like.

When the UE 1 has a role of the direct communication data transmission,the UE 1 transmits direct communication data and the UE 2 receivesdirect communication data. The transmission and the reception of the UE1 and the UE 2 may be reversed. The direct communication transmissionfrom the UE 1 may be received by one or more UEs such as UE2.

The D2D discovery and the D2D communication are not associated with eachother and independently defined. That is, the in groupcast and broadcastdirect communication, the D2D discovery is not required. As such, whenthe D2D discovery and the D2D communication are independently defined,the UEs need to recognize the adjacent UEs. In other words, in the caseof the groupcast and broadcast direct communication, it is not requiredthat all of the reception UEs in the group are close to each other.

A physical sidelink shared channel (PSSCH) may be defined as a channeltransmitting D2D direct communication data. Further, a physical sidelinkcontrol channel (PSCCH) may be defined as a channel transmitting controlinformation (for example, scheduling assignment (SA) for the directcommunication data transmission, a transmission format, and the like)for the D2D direct communication. The PSSCH and the PSCCH may reuse thePUSCH structure.

A method of allocating the resource for D2D direct communication may usetwo modes mode 1 and mode 2.

Mode 1 means a mode of scheduling a resource used for transmitting dataor control information for D2D direct communication. Mode 1 is appliedto in-coverage.

The eNB sets a resource pool required for D2D direct communication.Here, the resource pool required for D2D direct communication may bedivided into a control information pool and a D2D data pool. When theeNB schedules the control information and the D2D data transmissionresource in the pool set to the transmission D2D UE by using the PDCCHor the ePDCCH, the transmission D2D UE transmits the control informationand the D2D data by using the allocated resource.

The transmission UE requests the transmission resource to the eNB, andthe eNB schedules the control information and the resource fortransmission of the D2D direct communication data. That is, in the caseof mode 1, the transmission UE needs to be in an RRC_CONNECTED state inorder to perform the D2D direct communication. The transmission UEtransmits the scheduling request to the eNB and a buffer status report(BSR) procedure is performed so that the eNB may determine an amount ofresource required by the transmission UE.

The reception UEs monitor the control information pool and mayselectively decode the D2D data transmission related with thecorresponding control information when decoding the control informationrelated with the reception UEs. The reception UE may not decode the D2Ddata pool according to the control information decoding result.

Mode 2 means a mode in which the UE arbitrarily selects the specificresource in the resource pool for transmitting the data or the controlinformation for D2D direct communication. In the out-of-coverage and/orthe edge-of-coverage, the mode 2 is applied.

In mode 2, the resource pool for transmission of the control informationand/or the resource pool for transmission of the D2D directcommunication data may be pre-configured or semi-statically set. The UEreceives the set resource pool (time and frequency) and selects theresource for the D2D direct communication transmission from the resourcepool. That is, the UE may select the resource for the controlinformation transmission from the control information resource pool fortransmitting the control information. Further, the UE may select theresource from the data resource pool for the D2D direct communicationdata transmission.

In D2D broadcast communication, the control information is transmittedby the broadcasting UE. The control information explicitly and/orimplicitly indicate the position of the resource for the data receptionin associated with the physical channel (that is, the PSSCH)transporting the D2D direct communication data.

3) Synchronization

A D2D synchronization signal (alternatively, a sidelink synchronizationsignal) may be used so that the UE obtains time-frequencysynchronization. Particularly, in the case of the out-of-coverage, sincethe control of the eNB is impossible, new signal and procedure forsynchronization establishment between UEs may be defined.

The UE which periodically transmits the D2D synchronization signal maybe referred to as a D2D synchronization source. When the D2Dsynchronization source is the eNB, the structure of the transmitted D2Dsynchronization signal may be the same as that of the PSS/SSS. When theD2D synchronization source is not the eNB (for example, the UE or theglobal navigation satellite system (GNSS)), a structure of thetransmitted D2D synchronization signal may be newly defined.

The D2D synchronization signal is periodically transmitted for a periodof not less than 40 ms. Each UE may have multiple physical-layersidelink synchronization identities. The D2D synchronization signalincludes a primary D2D synchronization signal (alternatively, a primarysidelink synchronization signal) and a secondary D2D synchronizationsignal (alternatively, a secondary sidelink synchronization signal).

Before transmitting the D2D synchronization signal, first, the UE maysearch the D2D synchronization source. In addition, when the D2Dsynchronization source is searched, the UE may obtain time-frequencysynchronization through the D2D synchronization signal received from thesearched D2D synchronization source. In addition, the corresponding UEmay transmit the D2D synchronization signal.

Hereinafter, for clarity, direct communication between two devices inthe D2D communication is exemplified, but the scope of the presentinvention is not limited thereto, and the same principle described inthe present invention may be applied even to the D2D communicationbetween two or more devices.

As one of the D2D discovery schemes, there is a scheme in which all theUEs perform the discovery by a distribution method (hereinafter,referred to as ‘distributed discovery’). A scheme of performing thedistributive D2D discovery means a scheme in which all the UEsdistributively decides themselves to select the discovery resource andtransmits and receives the discovery message.

Hereinafter, in the specification, for the D2D discovery, signals(alternatively, messages) which are periodically transmitted by the UEsmay be referred to as a discovery message, a discovery signal, a beacon,and the like. Hereinafter, for convenience of description, the signalsare collectively referred to as the discovery messages.

In the distributive discovery, as a resource for transmitting andreceiving the discovery message by the UE, a separate dedicated resourcefrom a cellular resource may be periodically allocated. This will bedescribed with reference to FIG. 21 below.

FIG. 20 illustrates an example of a frame structure in which a discoveryresource to which the methods proposed in the specification may beapplied is allocated.

Referring to FIG. 20, in the distributive discovery scheme, among allthe cellular uplink frequency-time resource, a discovery subframe 2001(that is, a ‘discovery resource pool’) for discovery is fixedly(alternatively, dedicatedly) allocated, and the remaining area isconstituted by an existing LTE uplink wide area network (WAN) subframearea 2003. The discovery resource pool may be constituted by one or moresubframes.

The discovery resource pool may be periodically allocated at apredetermined interval (that is, a ‘discovery period’). Further, thediscovery resource pool may be repetitively set within one discoveryperiod.

FIG. 20 illustrates an example in which the discovery resource pool isallocated at a discovery period of 10 sec and 64 contiguous subframesare allocated to each discovery resource pool. However, the discoveryperiod and the size of the time/frequency resource of the discoveryresource pool are not limited thereto.

The UE selects a resource (that is, a ‘discovery resource’) fortransmitting the discovery message itself in the dedicatedly allocateddiscovery pool and transmits the discovery message through the selectedresource. This will be described with reference to FIG. 21 below.

FIG. 21 is a diagram schematically exemplifying a discovery process towhich the method proposed in the specification may be applied.

Referring to FIGS. 20 and 21, the discovery scheme is constituted bythree steps: sensing a resource for transmitting the discovery message(S2101), selecting a resource for the message transmission (S2103), andtransmitting and receiving the discovery message (S2105).

First, in the sensing of the resource for transmitting the discoverymessage (S2101), all the UEs performing the D2D discovery completelyreceive (that is, sense) the discovery message for 1 period (that is,the discovery resource pool) of the D2D discovery resource by adistributive method (that is, by themselves). For example, in FIG. 20,when the uplink bandwidth is 10 MHz, all the UEs fully receive (that is,sense) the discovery message which is transmitted in N=44 RB (since theentire uplink bandwidth is 10 MHz, 6 RBs for PUCCH transmission in atotal of 50 RBs are used) for K=64 msec (64 subframes).

In addition, in the selecting of the resource for transmitting thediscovery message (S2103), the UE classifies resources with a low energylevel among the sensed resources and randomly selects the discoveryresource in a predetermined range (for example, lower x % (x=anyinteger, 5, 7, 10, . . . )) among the resources.

The discovery resource may be constituted by one or more resource blockswith the same size and may be multiplexed to TDM and/or FDM in thediscovery resource pool.

In addition, in the transmitting and receiving of the discovery messageas the final process (S2105), the UE transmits and receives thediscovery message based on the discovery resource selected after onediscovery period (after P=10 seconds in the example of FIG. 20) andperiodically transmits and receives the discovery message according to arandom resource hopping pattern at a subsequent discovery period.

The D2D discovery procedure is proceeded even in the RRC_CONNECTED statewhere the UE is connected with the eNB and continuously performed evenin the RRC_IDLE state where the UE is not connected with the eNB.

Considering the discovery scheme, all the UEs sense all resources (thatis, the discovery resource pool) which are transmitted by neighboringUEs and randomly select the discovery resource in a predetermined range(for example, within lower x %).

Hereinafter, a D2D resource assignment method will be described indetails.

Referring to FIG. 22 and FIG. 23, D2D resource pool configuration andscheduling assignment (SA) methods will be described in details.

FIG. 22 illustrates one example of a D2D resource pool configurationwhere methods as disclosed herein are applicable.

Referring to FIG. 22, the D2D resource pool may be divided into N_(F)resource units in a frequency resource region and may be divided into NTresource units in a time resource region.

That is, an entire D2D resource pool may be defined as total N_(F)*N_(T)resource units. In this connection, each of N_(F) and N_(T) is a naturalnumber.

The resource unit 2210 may mean A number of subframes or B number of RBs(Resource Blocks). In this connection, each of A and B is a naturalnumber.

Further, the D2D resource pool may be repeated with a period of N_(T)subframes in the time resource region.

As shown in FIG. 22, one resource unit may be configured to repeatperiodically.

In an alternative, to get a diversity effect in the time or frequencyregion, an index of a physical resource unit mapping with one logicalresource unit may change into a predetermined pattern over time.

In this connection, the D2D resource pool may refer to a set of resourceunits which a D2D TX UE may use for D2D signal transmission.

Further, the D2D resource pool may have various configurations.

In one example, the D2D resource pool may be configured into three formsof resource pools as described below.

The three forms of resource pools may be distinguished from each otherbased on content of a D2D signal transmitted from an associated resourcepool.

In this connection, each resource pool may be separately configured.

(1) Scheduling Assignment (SA) Resource Pool

This resource pool may refer to a signal including a position of aresource used for transmission of a (subsequent) D2D data channel byeach sending UE, and information about modulation and coding scheme(MCS) or MIMO transmission scheme, etc. for decoding of a D2D datachannel. The SA may be multiplexed and transmitted together with D2Ddata on the same resource unit. In this case, the SA resource pool mayrefer to a resource pool on which the SA is multiplexed and transmittedtogether with the D2D data.

(2) D2D Data Channel Resource Pool

This resource pool may refer to a resource pool which a sending (ortransmitting) UE employs to send user data using a resource designatedby the SA. When the D2D data and SA together could be multiplexed andtransmitted on the same resource unit, a resource pool for the D2D datachannel may take a form on which only the D2D data channel istransmitted except SA information.

In this connection, the D2D data channel may refer to a D2Dcommunication channel.

That is, a resource element used to send SA information on an individualresource unit in the SA resource pool may be used for D2D datatransmission in the D2D data channel resource pool.

(3) Discovery (Message) Resource Pool

This resource pool may refer to a resource pool on which a sending UEsends message information about its ID, etc. to allow a neighboring UEto discover the sending UE.

Further, although contents of D2D signals are the same, D2D devices mayuse different resource pools based on transmission/reception attributesof the D2D signals.

For example, although D2D data channels or discovery messages are thesame, the resource pools may be different based on transmission timingdetermination schemes of the D2D signal (for example, one scheme wherethe D2D signal is transmitted at a receiving point of a synchronizationreference signal or one scheme where the D2D signal is transmitted byapplication of a constant timing advance (TA) at a receiving point of asynchronization reference signal), resource assignment schemes (forexample, one scheme where an eNB provides designation of a transmissionresource of an individual signal for the individual sending UE (mode 1)or one scheme where the individual sending UE selects an individualsignal transmission resource on its own in the pool (mode 2)), signalformats (for example, a number of symbols which each D2D signal takes inone subframe or a number of subframes used for D2D signal transmission).

As described above, the UE intending to send D2D data over the D2Dchannel may first select an appropriate resource in the SA resourcepool, and then send its SA via the selected resource.

In this connection, the selection criteria of the resource for the SAtransmission may be that a SA resource associated with a resource to beexpected not to be used for the SA transmission to another UE and/or forD2D data transmission in a subsequent subframe based on the SA ofanother UE may have a highest priority.

Additionally, the UE may select a SA resource associated with a D2D datatransmission resource expected to have a low interference level.

FIG. 23 illustrates one example of a D2D resource pool configurationwhere methods as disclosed herein are applicable.

As shown in FIG. 23, a SA resource pool 2310 may precede a D2D datachannel resource pool 2320.

Therefore, a receiving UE may first attempt to detect the SA, and, whenthere is D2D data to be required to be received thereby, may attempt toreceive the D2D data on the detected SA and associated D2D dataresource.

Referring to FIG. 23, the SA resource pool and the subsequent datachannel resource pool may be alternated repeatedly.

Further, a period of the SA resource pool appearance may be referred toas a SA period 2330.

That is, the SA period 2330 may be defined as a sum of one SA resourcepool duration and one data channel resource pool duration.

Hereinafter, methods for reducing interference or collision occurring inthe SA (Scheduling Assignment) transmission for the D2D communication asdisclosed herein will be described with reference to related drawings.

FIG. 24 is a schematic view of one example of a wireless communicationsystem where methods as disclosed herein are applicable.

As shown in FIG. 24, the present disclosure may provide methods fordetermining resource for device-to-device direct communication (D2Dcommunication). That is, the present disclosure may provide methods fordetermining resource for communication between UE1 and UE2 when UE1 andUE2 communicate with each other over a direct wireless channel (D2D linkor side link 2410).

In this connection, UE(UE1, UE2) may refer to a user device. However,when a network equipment acting as eNB communicate a signal using theD2D communication scheme, the network equipment acting as eNB may bealso considered as an UE.

It may be assumed that UE1 is a sending device (TX UE), and UE2 is areceiving device (RX UE) unless otherwise indicated.

Therefore, the UE1 may be configured to select a resource unit as aspecific resource in a resource pool indicating a set of resources andthen to send a D2D signal using the selected resource unit.

Further, the UE2 may be configured to preconfigure the resource pool forthe signal transmission by the UE1, and to detect the D2D signal sent bythe UE1 in the configured resource pool.

In this connection, when the UE1 is in-network coverage of a basestation, the base station may inform the UE1 of the resource pool. Whenthe UE1 is out-of-network coverage of the base station, another UE mayinform the UE1 of the resource pool or the resource pool may bepredetermined as a given resource.

In this connection, when another UE informs the UE1 of the resourcepool, said another UE may be a cluster header(CH) UE (or representativeUE) or as a UE (relay UE) located at a coverage border.

As described above, the resource pool may be formed of a plurality ofresource units. Each UE may select one or more resource units, and mayuse the selected resource unit for D2D signal transmission.

In this connection, the D2D signal transmission may refer to D2D controlindicator transmission, D2D data transmission, etc. wherein the controlindicator may include SA, etc.

That is, the D2D signal transmission may refer to transmission of allsignals from the D2D TX UE to the D2D RX UE.

Further, SA resource determination methods as described later may beapplied not only to SA transmission in the D2D communication but also toall systems employing the SA.

In particular, the SA resource determination methods as described latermay be more usefully applied to a system performing the schedulingassignment in a distributed manner.

FIG. 25 illustrates one example of a SA resource pool where methods asdisclosed herein are applicable, and a SA transmission method.

The SA resource pool may be mainly divided into a contention-basedregion where a SA resource is determined in a contention manner, and anon-contention-based region where a SA resource is determined in anon-contention manner.

As used herein, the non-contention-based region may be indicated a s ‘SAresource pool #1’ while the contention-based region may be indicated as‘SA resource pool #2(2510)’.

In the SA resource pool #1, the TX UE may send the SA withoutmeasurement information.

To the contrary, in the SA resource pool #2, the TX UE may send the SAusing the measurement information or a statistical method.

Hereinafter, method for suppressing collisions which otherwise willoccur due to the SA transmission in the SA resource pool #2 will bedescribed in details.

First, in order to solve the collision between SA resources in the SAresource pool #2, there is provided a method using random backoff.

In the D2D communication, the SA transmission may be conducted after afollowing procedure.

First, the sending UE may acquire the D2D resource pool for D2Dcommunication.

The UE may acquire the D2D resource pool from the base station or aspecific UE or by a previous receipt of information about the resourcepool.

As described above, the resource pool may include a SA resource pool, adata resource pool, a discovery resource pool, etc.

Thereafter, the UE may perform a D2D synchronization procedure with thebase station or another UE.

The another UE may be an UE with the largest transmission signalstrength and may be a predefined CH UE or representative UE.

Thereafter, the UE

may send the SA to another UE and send D2D data to the another UE basedon the SA.

The above-described procedures (resource pool acquisition,synchronization, etc.) prior to the SA transmission may be appliedcommonly to methods as described later, and descriptions thereof may beomitted hereinafter.

In this connection, the collision between the SA resources may due to asituation where the TX UEs send the SAs over the same SA resource.

The random backoff scheme may refer to a method for determining aresource for SA transmission, wherein when multiple contention windows(CWs) 2511 are present in the SA resource pool #2, each Tx UE may selecta random backoff value, and may contend with another Tx UEs in acontention window corresponding to the selected random backoff value.

Using the random backoff method, there may be still a collision betweenthe SA resources in each contention window.

Therefore, in order to reduce the collision in each CW, each Tx UE maynot send only one designated SA but may send repeatedly multiple SAs inthe SA resource pool #2.

In one example, each TX UE may send the SA in the SA resource pool fourtimes.

In this connection, the transmission of the multiple SAs in the SAresource pool #2 may mean multiple transmissions of the SA in onecontention window by the TX UE or multiple transmissions of the SA usingmultiple contention windows by the TX UE.

The contention window (CW) may mean one or more subframes (or TTI).

Next, a method for transmitting multiple SAs by the TX UE will bedescribed in details.

Transmission of the multiple SAs may be construed to transmit the SArepeatedly or to re-transmit the SA.

Hereinafter, for the sake of convenience, transmission of multiple SAsmay be construed as re-transmission of the SA for the situation that,after the SA initial transmission, the SA may be re-transmitted usingspecific information.

Before the SA transmission, the resource pool acquisition, and D2Dsynchronization may be conducted. After the SA transmission, the datatransmission may be conducted.

Further, it may be assumed that frequency and time axes resourceassignment of the D2D data channel (or D2D communication channel) may bedetermined implicitly based on the SA transmission.

That is, it may be assumed that, when information about the resourceassignment of the frequency and time axes for the SA transmission isknown, information about the resource assignment of frequency and timeaxes of the D2D data channel is also known.

When it is defined that the UE sends only one SA (no transmission of themultiple SAs) in the SA resource pool #2 as shown in FIG. 25, the SAresource used by the TX UE once in the Tx specific CW may be not used ina next contention window but remain in an empty state.

In this case, due the empty SA resource, the SA resources available forthe UEs may be deficient, and, thus, there will occur collisions betweenthe UEs using the same SA resource in the same contention window (e.g.,there occurs a collision in a CW #0 2511 and a CW #2 2513 in FIG. 25).

Therefore, using a non-used and empty SA resource in the CWappropriately, the collision which will otherwise occur in using thesame SA resource in the same CW may be reduced.

Hereinafter, a method for transmitting and re-transmitting a SA by TXUEs using a non-used and empty SA resource in a CW appropriately will bedescribed in details.

The Tx UE may determine whether SA transmission or re-transmission isconducted on a SA resource in a CW, using informant about SA resourceusage in the SA resource pool #1 and SA information measured (or used)in previous CWs in the SA resource pool #2, etc.

In this connection, the previous CWs may refer to CWs before a CW inwhich the TX UE currently sends the SA.

Further, in case of the SA re-transmission, the TX UE may determinewhether to conduct re-transmission of the SA at the same resourcelocation as that in the SA initial transmission or at a differentresource location from that in the SA initial transmission, using themeasured SA information.

In this connection, the resource location for the SA initialtransmission being the same as the resource location for the SAre-transmission may mean the same resource locations on a time and afrequency in each of different CWs.

As for a resource on which a specific Tx UE(s) sends the SA, aninterference for the resource may be detected in a subsequent CW.

In this case, some TX UE may give up SA re-transmission at the sameresource location in a subsequent CW as that of the resource for theprevious SA transmission, and find another suitable SA resource for SAre-transmission.

However, at least one TX UE may send the SA at the resource location inwhich the SA re-transmission is given up.

Therefore, it may be desirable for the TX UE to determine the SAtransmission resource not only by measuring the specific contentionwindow, but also by checking collectively all of the CWs measured beforethe SA transmission.

Selection Criteria of Resource for SA Transmission

Next, selection criteria of a SA resource for SA initial transmissionand SA re-transmission will be described.

For the SA resources in the SA resource pool #2, an effective energyvalue to allow a determination of SA transmission occurrence may bemeasured in some CWs, while a low energy value to disallow adetermination of SA transmission occurrence may be measured in the otherCWs.

In this connection, the low energy value may refer to a thermal noiselevel or a receiving energy value nearby the thermal noise level.

That is, the TX UE may determine a resource for the SA transmission bymeasuring receiving energy levels in CWs and comparing all of measuredreceiving energy values in the CWs predicted to have SA transmissionoccurrences.

In this connection, in order to determine whether the SA transmissionoccurs, there are provided several threshold values in terms of thereceiving energy level measurements.

That is, the TX UE may determine whether the SA transmission occurs bycomparing between the defined threshold value and receiving energylevel, and then may determine the resource for the SA transmission basedon the above determination.

A first threshold value may be defined as a threshold value r0 for anull resource when the SA transmission does not occur.

A second threshold value may be defined as a threshold value r1 toindicate a maximum interference at which the SA transmission isacceptable.

In this connection, a relationship between the threshold value r0 andthreshold value r1 may be expressed as follows:threshold value r0≤threshold value r1  [equation 16]

Now, a method for determining a SA resource for SA initial transmissionand SA re-transmission using the defined threshold values will bedescribed.

First, a method for determining a SA resource for SA initialtransmission will be described.

For the SA initial transmission, the TX UE may select one resource amongeffective resources satisfying that a receiving energy value in a CW issmaller than the threshold value r0 (Erx<r0). Then, the TX UE may sendthe SA using the selected resource. In this connection, the Erx mayindicate the receiving energy value.

When there is none of the effective resources satisfying that areceiving energy value in a CW is smaller than the threshold value r0(Erx<r0), the TX UE may select one resource among resources satisfyingErx<r1 and may send the SA using the selected resource.

When all of the resources satisfy Erx>=r1, the TX UE may give up SAtransmission in an associated CW, or select any resource and perform theSA transmission, or perform the SA transmission in another CW.

In this connection, when the TX UE selects any resource and performs theSA transmission, there is an interference in an associated resource,and, thus, the TX UE fails to perform the SA transmission.

Next, a method for determining a SA resource for SA re-transmission willbe described.

For the SA re-transmission, the TX UE may not be required to check thereceiving energy values for all of the SA resources unlike the SAinitial transmission.

That is, when the TX UE could check some or all of interferenceinformation for the SA resource used for the initial transmission, theTX UE may determine a resource for SA re-transmission using followingtwo ways:

(1) A first way is to perform the SA re-transmission by reusing the SAresource used for the SA initial transmission as maximally as possible.

That is, when a maximum interference level acceptable by the measuredreceiving energy for the SA resource used for the SA initialtransmission is equal to or smaller than a r1 value, the UE may selectthe associated SA resource and perform the SA re-transmission using theselected resource.

However, when the maximum interference level acceptable by the measuredreceiving energy for the SA resource used for the SA initialtransmission is larger than the r1 value, the TX UE may not select theSA resource used for the SA initial transmission but select anotherappropriate SA resource for the SA re-transmission.

(2) A second way is to perform the SA re-transmission by selecting a SAresource expected to have the smallest interference.

That is, the TX UE may compare between all of the receiving energyvalues not only for the SA resource used for the SA initial transmissionbut also SA resources in all SA resource regions, and may select a SAresource exhibiting the smallest interference (or an interference beingwithin the smallest interference+a, a>0) as the SA resource for the SAre-transmission.

SA Transmission Confirmation

Now, a method for confirming the SA transmission to distinguish betweenthe SA initial transmission and SA re-transmission.

In order to distinguish between the SA initial transmission and SAre-transmission, and, thus, to inform that there is no further SAtransmission, the TX UE may send the SA together with a confirmationflag contained therein.

In this way, due to the fact that the TX UE may send the SA togetherwith a confirmation flag contained therein, the UE may consider only SAswith completed confirmation thereof as an effective transmissionresource.

The Confirmation flag may have a following form.

(1) Some bits (1 bit to several bits) among SA information bits may beused as a confirmation flag.

In this case, the confirmation flag may be encoded together with the SAinformation.

Therefore, the UE may confirm the SA transmission only after decodingthe SA.

For example, when the confirmation field indicates ‘0’, the SAtransmission is not confirmed. When the confirmation field indicates‘1’, it is confirmed that the SA is sent to an associated resourcelocation, and data is sent to a data resource region associated with theSA transmission resource. That is, when the confirmation field indicates‘1’, it is confirmed that there is no further SA transmission.

(2) A separate component may be padded into the SA payload.

That is, a confirmation flag RE(s) associated with 1 to several Res(Resource Elements) may be inserted into an encoded SA payload.

For example, for the SA whose transmission is not confirmed, an energyfor RE(s) associated with the confirmation field may not be detected.

Alternatively, for the SA whose transmission is not confirmed, a lowenergy (e.g. background noise level) for RE(s) associated with theconfirmation field, as allows a determination of the RE(s) as an emptyRE(s) may be detected.

On the other hand, for the SA whose transmission is confirmed, an energyfor RE(s) associated with the confirmation field may be detected as asum of a transmission energy, and energies associated with a path decay,etc.

That is, using the above padding operation, the UE may estimate theinterference only via some Res without decoding all of the SAs.

However, When the separate component is padded into the SA payload, itmay not be correctly informed whether some Tx UEs confirm the SAtransmission.

Therefore, in this case, it may be desirable to employ the above (1)approach where some bits (1 bit to several bits) among SA informationbits are used as a confirmation flag.

When it is determined that the SA re-transmission is impossible, the TXUE may previously turn the confirmation flag ‘On’ and send the flag inthe SA initial transmission.

In this connection, the Tx UE turning the confirmation flag on may referto an UE which may not perform the SA re-transmission after the SAinitial transmission and, rather, assist in SA initial transmission andre-transmission operations by another Tx UE.

For example, when a random backoff value between 0 and (n−1) has (n−1)or (n−2), the SA re-transmission is impossible or incomplete. Thus, itmay be more preferable to confirm that the SA transmission has beencompleted at an initial transmission of the SA.

The impossible SA re-transmission may lead to an impossible furthercollision prevention attempt since a CW for the SA re-transmission is nolonger present in the SA resource pool.

The incomplete SA re-transmission may lead to a case that all UEs do nothave SA re-transmission chances but only some UEs can attempt to preventa collision via the SA re-transmission in the SA resource with apossibility of collisions of transmitted SA resources.

Due to the above impossible and/or incomplete SA transmission, the TxUEs turning the confirmation flag on sends the SA in a given CW but,thereafter, never send an additional SA re-transmission in the CW.

Therefore, another Tx UEs may detect the presence of the Tx UEs turningthe confirmation flag on and then may perform SA transmission withconsideration of the above.

SA Re-Transmission Method Using Probabilistic Scheme

Now, a method for preforming SA re-transmission using a probabilisticscheme will be described.

When multiple TX UEs simultaneously contend with each other for SAtransmission in the same CW, there may be a collision between some UEsfor the SA transmission.

In particular, when a number of UEs is larger than a number of SAresources, and the associated CWs are not sufficient, the collisionbetween the SA transmissions is inevitable.

When, in this way, the collision between the SA transmissions occurs, itis impossible for UEs performing the SA transmission to check SAtransmission information between them.

In this connection, when it is possible for UEs performing the SAtransmission to check SA transmission information (receiving energylevel for SA transmission) between them, the TX UEs may determinewhether to continue using a specific resource for the SA transmission orselect another resource for SA transmission.

To this end, the TX UEs should perform SA initial transmission in a CWcorresponding to a random backoff value selected initially by them and,then, perform SA re-transmission in the CW.

That is, the UEs which selects a ‘m” value among the random backoffvalues between 0 and (n−1), and, thus, select the same resource in a CW#m may perform SA re-transmission in CW #(m+1) to CW #(n−1).

In this connection, when the TX UE performs SA re-transmission in a CW#(m+1), it may dispense with a separate collision information.

That is, all TX UEs may determine whether to perform SA re-transmissionwith a P₀ probability in the CW #(m+1).

Remaining UEs (whose average values (expected values) are equal to anumber of all TX UEs*(1−P₀)) except the UEs (whose average values(expected values) are equal to a number of all TX UEs*P₀) performing theSA re-transmission in the CW #(m+1) may similarly determine whether toperform SA re-transmission with a P₁ probability in the CW #(m+2).

In this connection, when the TX UEs determines whether to perform SAre-transmission with the P₁ probability in the CW #(m+2), the TX UEs maydetermine whether to perform SA re-transmission with furtherconsideration of SA information re-sent in the CW #(m+1).

However, when any TX UE does not perform SA re-transmission or allrelated UEs perform SA re-transmission in the CW #(m+1), an interferenceinformation measurement in a previous CW may not be useful in afollowing CW.

Therefore, in order to perform SA re-transmission in the following CWusing the interference information measurement in the previous CW,following three approaches may be used.

In this connection, a situation when any TX UE does not perform SAre-transmission or all related UEs perform SA re-transmission in theprevious CW and, thus, interference information measurement in theprevious CW is not useful in the following CW may be referred to as‘worst case’ for the sake of convenience.

(1) In order to avoid the above-defined worst case in a first SAre-transmission CW, a probability P₀ may be determined which minimizes asum of a first probability for a first worst case where any TX UE doesnot perform SA re-transmission and a second probability for a secondworst case where all related UEs perform SA re-transmission.

In this connection, the P₀ indicates a probability for a worst casewhere all related UEs perform SA re-transmission in a CW #(m+1).

When there occur collisions between k UEs for the SA resource, aprobability for a worst case where all related UEs perform SAre-transmission in the CW #(m+1) is p₀ ^(k), and a probability for aworst case where any TX UE does not perform SA re-transmission in the CW#(m+1) is (1−P₀)^(k).

That is, in order to avoid the above two worst cases, the P₀ valueminimizing a Y value in a following equation 17 may be determined:y=P ₀ ^(k)(1−P ₀)^(k)  [equation 17]

In this connection, the P₀ value minimizing the Y value in the equation17 is a value which turns a y′ value into zero in a following equation18 which is a differential of the equation 17:y′=k×P ₀ ^(k-1) −k×(1−P ₀)^(k-1)  [equation 18]

In this connection, y′ indicates a differential of y. Therefore, whenk≠0, the P₀ value which turns the y′ value into zero in the equation 18is 0.5. This may also be confirmed with reference to FIG. 26.

FIG. 26 is a graph illustrating one example of SA re-transmissionprobability values in a specific CW for a SA re-transmission methodusing the probabilistic scheme as disclosed herein.

Therefore, in order to minimize only the worst cases in a CW #(m+2) as afollowing CW, it may be set similarly such that the P₁=0.5.

Generally, the above worst cases may be suppressed by setting a SAre-transmission probability P_((j-1)) to 0.5 in a CW #(m+j) as aspecific CW in the SA resource pool #2.

(2) When a number k of UEs having collisions in a CW and a number q ofremaining CWs are known, a SA re-transmission probability may bedetermined such that the k UEs are uniformly distributed within theremaining q CWs.

That is, the TX UEs may perform SA re-transmission in each CW based onthe probability determined based on the approach (2).

That is, the k UEs may be uniformly distributed within the remaining CWsin following two ways:

(A) First, k UEs may be uniformly distributed across k CWs (within asmallest CW). In this connection, when each UE is selected with a Pprobability per CW, the probability P that each UEs may be distributedin each CW may be defined as a following equation 19.

$\begin{matrix}{P = {{k!} \cdot P^{k} \cdot {\prod\limits_{i = 0}^{k - 1}\left( {1 - P} \right)^{i}}}} & \left\lbrack {{equation}\mspace{14mu} 19} \right\rbrack\end{matrix}$

In this connection, when P=2/(k+1), the equation 19, that is, theprobability value is maximum.

That is, each UE may perform SA re-transmission with the P=2/(k+1)probability in each CW.

In this connection, each SA re-transmission probability P₀, P₁, . . . ,etc. in each CW may be appropriately adjusted depending on variations ofa number (k) of UEs undergoing the collision.

(B) Second, k UEs may be uniformly distributed across q CWs (remainingall CWs).

Actually, it may be possible that the q value is larger or smaller thanthe k value.

When the q value is smaller than the k value, in spite of the SAre-transmission, the collision is inevitable or some UEs should give upthe SA re-transmission. For this reason, hereinafter, this case will beexcluded. That is, the case when the q value is not smaller than the kvalue will be considered below.

The P value maximizing the probability value that the UEs may beuniformly distributed without the overlapping CW may be set based oneach k value and q value as a following table 8.

Similarly, each re-transmission probability P₀, P₁, . . . , etc. in eachCW may be appropriately adjusted depending on a number (k) of UEsundergoing the collision and a number (q) of the remaining CWs.

TABLE 8 q k 2 3 4 5 6 7 8 2 0.667 0.571 0.505 0.454 0.413 0.380 0.352 3— 0.500 0.439 0.393 0.357 0.328 0.305 4 — — 0.400 0.358 0.325 0.2990.277 5 — — — 0.333 0.303 0.278 0.258 6 — — — — 0.285 0.262 0.243 7 — —— — — 0.250 0.232 8 — — — — — — 0.222

When only a number (q) of the remaining CWs is known, the SAre-transmission probability may be determined such that the UEs may beuniformly distributed across the q CWs.

That is, when it is most preferable that the UEs to perform SAre-transmission is uniformly distributed across the remaining CWs, theSA re-transmission probability may be determined using a number of theremaining CWs.

The UEs performing SA (initial) transmission in a CW #m may perform SAre-transmission with a 1/(n−m−1) probability in a CW #(m+1).

On the other hand, among the UEs performing the SA (initial)transmission in the CW #m, UEs not performing the SA re-transmission inthe CW #(m+1) could additionally check SA transmission relatedinformation in the CW #(m+1). Thus, using the SA transmission relatedinformation in the CW #(m+1), the UEs not performing the SAre-transmission in the CW #(m+1) may perform SA re-transmission with a1/(n−m−2) or 1/(q−1) probability in a CW #(m+2).

Generally, the UEs may perform SA re-transmission with a 1/(n−(m+i)) or1/(q−(i−1)) probability in the CW #(m+i).

As described above, some of the UEs performing the SA (initial)transmission in the CW #m may perform the SA re-transmission (in aprobabilistic manner) in the CW #(m+1) at the same resource location asthat in the CW #m.

Further, the remaining UEs not performing the SA re-transmission in theCW #(m+1) may attempt performing the SA re-transmission in a CW #(m+2)or a subsequent CW thereof. Thus, the UEs may measure a receiving energyin the CW #(m+1) (the energy including a portion of interferenceoccurring in the CW #m) and may use the energy measurement for the SAre-transmission.

In this connection, the UEs may determine whether to perform the SAre-transmission with P₁ probability in the CW #(m+2). That is, a numberof UEs calculated as the P₁ of a number of the UEs may perform the SAre-transmission in the CW #(m+2).

In this connection, the P₁ may be the same as or different from the P₀.

In this connection, as shown in FIG. 27, the UEs performing the SAre-transmission may determine, using interference measurementinformation in the previous CW, whether to perform SA re-transmission atthe same resource location as that in the previous CW or perform SAre-transmission using another optimal resource.

When the UEs perform the SA re-transmission using another optimalresource, the UEs may select the optimal resource for the SAre-transmission using the minimum received energy, etc.

The UE may repeat the above process until the contention window ends.

FIG. 27 illustrates one example of a SA re-transmission method asdisclosed herein.

CW Selection Probability for SA Initial Transmission

Next, a probabilistic method for selecting a CW (Contention Window) byan UE for SA initial transmission will be described.

The TX UE may determine a random backoff value corresponding to a CW tobe accessed for the SA transmission based on whether to perform furtherSA re-transmission in following two different schemes.

First, the TX UE may access all CWs with the same probability for the SAtransmission.

That is, when n CWs are present in the SA resource pool #2, all TX UEsmay equally determine an access probability as 1/n for each CW among CW#0 to CW #(n−1).

However, this scheme may not be suitable for the SA re-transmission bythe TX UE.

This is because, for the SA re-transmission, some UEs may re-access a CWsubsequent to a CW accessed by the UEs for the SA initial transmission.

Therefore, the TX UE may determine the access probability to each CW forSA transmission with further consideration of a following second scheme.

That is, the TX UE may not access to each CW with the same probabilitywhich is 1/n. Rather, the TX UE may raise a CW access (or selection)probability when an associated CW is more preceding, while the TX UE maylower a CW access (or selection) probability when an associated CW isless preceding, that is, more succeeding.

For example, it may be assumed that the access probability by the TX UEto CW #0 is referred to as P₀, the access probability by the TX UE to CW#1 is referred to as P₁, the access probability by the TX UE to CW#(n−1) is referred to as P_((n-1)), and so on. In this connection, itmay be configured such that each probability may be set to comply with afollowing equation 20.P ₀ ≥P ₁ ≥ . . . ≥P _(n-1)  [equation 20]

In this connection, when the TX UE performs SA initial transmission in aCW #(n−1), the TX UE could not perform SA re-transmission thereafter.

Further, when the TX UE performs SA initial transmission in a CW #(n−2),the TX UE could perform SA re-transmission in a CW #(n−1) or may notperform SA re-transmission in a CW #(n−1). Thus, two cases may beavailable.

Similarly, when the TX UE performs SA initial transmission in a CW#(n−3), the TX UE may or not perform SA re-transmission in a CW #(n−2)or a CW #(n−1). Thus, four cases may be available.

Generally, when the SA resource pool includes n CWs, a total number ofcases for SA initial transmission and SA re-transmission may be definedas a following equation 21.2^(n-1)  [equation 21]

In this connection, a total number of cases that the TX UE performs SAinitial transmission in a CW #m, and performs or does not perform SAre-transmission in a subsequent CW may be defined as a followingequation 22:2^((n-1)-m)  [equation 22]

Therefore, a probability Pm that the TX UE performs SA initialtransmission in a CW #m may be defined as a following equation 23.

$\begin{matrix}\frac{2^{{({n - 1})} - m}}{2^{n - 1}} & \left\lbrack {{equation}\mspace{14mu} 23} \right\rbrack\end{matrix}$

FIG. 28 illustrates one example of a flow-chart of a SA transmission andSA re-transmission method as disclosed herein.

First, a TX UE may acquire a resource pool for D2D communication(S2810).

In this connection, the TX UE may acquire the resource pool for D2Dcommunication from a base station or another device or via a pre-input.

As used herein or in claims, the TX UE may be referred to as a firstdevice, and a RX UE may be referred to as a second device.

The resource pool includes a SA (scheduling assignment) resource poolindicating a resource region for SA transmission, a data resource poolindicating a resource region for D2D data transmission, and a discoveryresource pool indicating a resource region for discovery messagetransmission, etc.

The SA resource pool includes at least one of first and second SAresource pools, wherein in the first pool (SA resource pool #1), a SAresource is determined in a non-contention manner, and, in the secondpool (SA resource pool #2), a SA resource is determined in a contentionmanner.

Further, the second SA resource pool may include one or more contentionwindows (CWs).

The CW may indicate one or more sub-frames.

Thereafter, the TX UE may perform D2D synchronization with a basestation or specific device (S2820).

The specific device may include a cluster header (CH) device orrepresentative device in a D2D device group or a device at a coverageborder.

The D2D synchronization process may be referred to the abovedescription.

Thereafter, the TX UE may send a SA (scheduling assignment) to thesecond device or RX UE using the SA resource pool, wherein the SAincludes information related to D2D data transmission (S2830).

The SA (scheduling assignment) sent to the second device furtherincludes a SA confirmation flag field to indicate whether a further SAtransmission is present after the SA transmission.

The SA confirmation flag may be used to distinguish between the SAinitial transmission or SA re-transmission.

In this connection, the first device sending (or transmitting) the SA(scheduling assignment) to the second device comprises the first devicesending multiple SAs in the second SA resource pool to the seconddevice.

In this connection, the SA transmission S2830 to the RX UE may includepreforming SA initial transmission in a first CW in the second SAresource pool, and performing SA re-transmission in a second CW afterthe first CW.

The SA initial transmission and the SA re-transmission to the receivingdevice will be described in details with reference to FIG. 29.

The TX UE may perform the SA initial transmission and re-transmissionbased on SA interference information measured in previous CWs to acurrent CW for the SA transmission and/or the first SA resource poolinformation.

As described above, the RX UE may be referred to as the second device.

Thereafter, the TX UE may send D2D data to the RX UE based on the SA(S2840).

FIG. 29 illustrates another example of a flow-chart of a SA transmissionand SA re-transmission method as disclosed herein.

FIG. 29 illustrates a specific method for sending SA in a contentionmanner, that is, using the SA resource pool #2.

Operations S2910, S2920 and S2950 may be the same as the operationsS2810, S2820 and S2840 and, thus, descriptions thereof may be omitted.

After S2920, the TX UE may send a first SA (scheduling assignment) tothe RX UE using a first CW in the SA resource pool #2 (S2930).

That is, the TX UE may perform the SA initial transmission.

Thereafter, the TX UE may perform re-transmission corresponding to thefirst SA transmission in a second CW in the SA resource pool #2 (S2940).

The second CW may refer to a CW after the first CW.

Further, for the SA initial transmission, the TX UE may (1) determine arandom backoff value corresponding to a CW for the SA initialtransmission; and (2) perform the SA initial transmission in the CWcorresponding to the determined random backoff value.

The random backoff values may be determined with the same probabilityfor all CWs in the second SA resource pool; or the random backoff valuesmay be determined such that probabilities thereof are based onprecedence of corresponding CWs.

The specific method for determining the random backoff value may bereferred to the above descriptions.

In another embodiment, the first device or TX UE performing the SAinitial transmission comprises: comparing a receiving energy value forthe first CW with a predetermined first threshold value or secondthreshold value; and determining whether to perform the SA initialtransmission based on the comparison.

The first threshold value is an energy level corresponding to an emptyresource and the second threshold value is a maximum interference levelat which the SA transmission is acceptable.

When the receiving energy value is smaller than the predetermined firstthreshold value, the first device or TX UE performs the SA initialtransmission using the SA resource in the first CW.

When the receiving energy value is larger than the predetermined secondthreshold value, the first device or TX UE gives up performing the SAinitial transmission in the first CW.

Further, in order for the TX UE to perform the SA re-transmission, (1)the TX UE computes a probability value for the SA re-transmission in thesecond CW; and performs the SA re-transmission in the second CW based onthe computed probability value.

In this connection, the probability value is determined as a valueminimizing a sum of a probability that all devices perform SAre-transmission in the second CW and a probability that any device doesnot perform SA re-transmission in the second CW.

In an alternative, the probability value is determined withconsideration of a number of devices undergoing collisions for SAtransmission and/or a number of remaining CWs.

The specific method for performing SA re-transmission using theprobability value may be referred to the above descriptions.

FIG. 30 illustrates another example of a flow-chart of a SA transmissionand SA re-transmission method as disclosed herein.

FIG. 30 illustrates a method for selecting a SA resource pool based onSA transmission change and performing the SA transmission using theselected resource.

Operations S3010, S3020 and S3060 may be the same as the operationsS2810, S2820 and S2840 in FIG. 28 and, thus, descriptions thereof may beomitted.

After S3020, the TX UE may select a SA resource pool for SA transmissionbased on SA transmission change (S3030).

The SA transmission change may refer to a change between thenon-contention based SA transmission scheme and the contention-based SAtransmission scheme.

Hereinafter, one example will be described in which the SA transmissionchange refers to a change from the non-contention based SA transmissionscheme to the contention-based SA transmission scheme.

That is, when the TX UE detects the SA transmission, the TX UE may sendSA using the SA resource pool #2 (S3040).

To be specific, the TX UE may send a first SA (scheduling assignment) tothe RX UE in a first CW in the SA resource pool #2 (S3041).

That is, the TX UE may perform the SA initial transmission.

Thereafter, the TX UE may preform SA re-transmission corresponding tothe first SA transmission in a second CW in the SA resource pool #2(S3042).

The second CW may refer to a CW after the first CW.

To the contrary, when the TX UE does not detect the SA transmissionchange, the TX UE may perform SA transmission using the SA resource pool#1 (S3050).

Thereafter, the TX UE may send D2D data to the RX UE using the SAresource pool determined based on whether there is SA transmissionchange (S3060).

The specific method for the SA initial transmission and SAre-transmission may be referred to the above descriptions.

Device Using the Present Invention

FIG. 31 illustrates a block diagram of a wireless communication devicewhere methods as disclosed herein are applicable.

Referring to FIG. 31, the wireless communication system may include abase station 3110 and multiple devices 3120 located in a coverage of thebase station 3110.

The base station 3110 may include a processor 3111, a memory 3112, and aRF unit (radio frequency unit) 3113. The processor 3111 may beconfigured to execute the functions, procedures, and/or methods asdescribed with reference to FIG. 1 to FIG. 30. Layers of the wirelessinterface protocol may be implemented by the processor 3111. The memory3112 may be coupled to the processor 3111 to store therein variousinformation to drive the processor 3111. The RF unit 3113 may be coupledto the processor 3111 to communicate a RF signal.

The device 3120 may include a processor 3121, a memory 3122, and a RFunit 3123. The processor 3121 may be configured to execute thefunctions, procedures, and/or methods as described with reference toFIG. 1 to FIG. 30. Layers of the wireless interface protocol may beimplemented by the processor 3121. The memory 3122 may be coupled to theprocessor 3121 to store therein various information to drive theprocessor 3121. The RF unit 3123 may be coupled to the processor 3121 tocommunicate a RF signal.

The memories 3112, 3122 may be located in or out of the processors 3111,3121 respectively. The memories 3112, 3122 may be coupled to theprocessors 3111, 3121 respectively via well-known means. Further, thebase station 3110 and/or device 3120 may have a single antenna ormultiple antennas.

The above Description of Embodiments includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichmethods, apparatuses, and systems discussed herein may be practiced.These embodiments are also referred to herein as “examples.” Suchexamples may include elements in addition to those shown or described.However, the present inventors also contemplate examples in which onlythose elements shown or described are provided. Moreover, the presentinventors also contemplate examples using any combination or permutationof those elements shown or described (or one or more aspects thereof),either with respect to a particular example (or one or more aspectsthereof), or with respect to other examples (or one or more aspectsthereof) shown or described herein.

The flowchart and block diagrams in the FIGS, illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousaspects of the present disclosure. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, may be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, a non-transitorycomputer readable storage medium, or any other machine readable storagemedium wherein, when the program code is loaded into and executed by amachine, such as a computer, the machine becomes an apparatus forpracticing the various techniques. In the case of program code executionon programmable computers, the computing device may include a processor,a storage medium readable by the processor (including volatile andnonvolatile memory and/or storage elements), at least one input device,and at least one output device. The volatile and non-volatile memoryand/or storage elements may be a RAM, an EPROM, a flash drive, anoptical drive, a magnetic hard drive, or another medium for storingelectronic data. The base station) and UE (or other mobile station) mayalso include a transceiver component, a counter component, a processingcomponent, and/or a clock component or timer component. One or moreprograms that may implement or utilize the various techniques describedherein may use an application programming interface (API), reusablecontrols, and the like. Such programs may be implemented in a high-levelprocedural or an object-oriented programming language to communicatewith a computer system. However, the program(s) may be implemented inassembly or machine language, if desired. In any case, the language maybe a compiled or interpreted language, and combined with hardwareimplementations.

It should be understood that many of the functional units described inthis specification may be implemented as one or more components, whichis a term used to more particularly emphasize their implementationindependence. For example, a component may be implemented as a hardwarecircuit comprising custom very large scale integration (VLSI) circuitsor gate arrays, off-the-shelf semiconductors such as logic chips,transistors, or other discrete components. A component may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices, orthe like.

Components may also be implemented in software for execution by varioustypes of processors. An identified component of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object, aprocedure, or a function. Nevertheless, the executables of an identifiedcomponent need not be physically located together, but may comprisedisparate instructions stored in different locations that, when joinedlogically together, comprise the component and achieve the statedpurpose for the component. Indeed, a component of executable code may bea single instruction, or many instructions, and may even be distributedover several different code segments, among different programs, andacross several memory devices. Similarly, operational data may beidentified and illustrated herein within components, and may be embodiedin any suitable form and organized within any suitable type of datastructure. The operational data may be collected as a single data set,or may be distributed over different locations including over differentstorage devices, and may exist, at least partially, merely as electronicsignals on a system or network. The components may be passive or active,including agents operable to perform desired functions.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments may be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to complywith 37 C.F.R. § 1.72(b), to allow the reader to quickly ascertain thenature of the technical disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Also, in the above Description of Embodiments,various features may be grouped together to streamline the disclosure.This should not be interpreted as intending that an unclaimed disclosedfeature is essential to any claim. Rather, inventive subject matter maylie in less than all features of a particular disclosed embodiment.Thus, the following claims are hereby incorporated into the Descriptionof Embodiments as examples or embodiments, with each claim standing onits own as a separate embodiment, and it is contemplated that suchembodiments may be combined with each other in various combinations orpermutations. The scope of the invention should be determined withreference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

Although the present disclosure has been described with the exampleswhere the resource assignment method is applied to 3GPP LTE/LTE-A systemin a wireless communication system, the present disclosure may beapplied to examples where the resource assignment method is applied toother wireless communication systems than the 3GPP LTE/LTE-A system.

The invention claimed is:
 1. A method for performing, by a first device,device-to-device (D2D) communication in a wireless communication system,the method comprising: acquiring a resource pool for the D2Dcommunication, wherein the resource pool includes a schedulingassignment (SA) resource pool indicating a resource region for SAtransmission and a data resource pool indicating a resource region forD2D data transmission; performing D2D synchronization with a basestation or a specific device; transmitting an SA to a second deviceusing the SA resource pool, wherein the SA includes information relatedto D2D data transmission; and transmitting D2D data to the seconddevice, wherein the SA resource pool includes at least one of a first SAresource pool or a second SA resource pool, wherein in the first SAresource pool, a SA resource is determined in a non-contention manner,and, in the second SA resource pool, a SA resource is determined in acontention manner, wherein the second SA resource pool includes one ormore contention windows (CWs), and wherein, in the second SA resourcepool, multiple SAs are transmitted to the second device.
 2. The methodof claim 1, wherein, if, in the second SA resource pool, multiple SAsare transmitted to the second device, transmitting the SA to the seconddevice comprises: performing SA initial transmission in a first CW inthe second SA resource pool; and performing SA re-transmission in asecond CW following the first CW.
 3. The method of claim 2, whereinperforming the SA initial transmission comprises: determining a randombackoff value corresponding to a CW for the SA initial transmission; andperforming the SA initial transmission in the CW corresponding to thedetermined random backoff value.
 4. The method of claim 3, wherein therandom backoff values are determined with the same probability for allCWs in the second SA resource pool; or the random backoff values aredetermined such that probabilities thereof are based on precedence ofcorresponding CWs.
 5. The method of claim 2, wherein performing the SAre-transmission comprises: computing a probability value for the SAre-transmission in the second CW; and performing the SA re-transmissionin the second CW based on the computed probability value.
 6. The methodof claim 5, wherein the probability value is determined as a valueminimizing a sum of a probability that all devices perform SAre-transmission in the second CW and a probability that any device doesnot perform SA re-transmission in the second CW.
 7. The method of claim5, wherein the probability value is determined with consideration of atleast a number of devices undergoing collisions for SA transmission or anumber of remaining CWs.
 8. The method of claim 2, wherein the SAinitial transmission and the SA re-transmission are conducted based onat least an SA resource interference measured in previous CWs to acurrent CW for the SA transmission or information regarding the first SAresource pool.
 9. The method of claim 2, wherein performing the SAinitial transmission comprises: comparing a receiving energy value forthe first CW with a predetermined first threshold value or apredetermined second threshold value; and determining whether to performthe SA initial transmission based on the comparison, wherein the firstthreshold value is an energy level corresponding to an empty resourceand the second threshold value is a maximum interference level at whichthe SA transmission is acceptable.
 10. The method of claim 9, whereinwhen the receiving energy value is smaller than the predetermined firstthreshold value, the first device performs the SA initial transmissionusing the SA resource in the first CW.
 11. The method of claim 10,wherein when the receiving energy value is larger than the predeterminedsecond threshold value, the first device gives up performing the SAinitial transmission in the first CW.
 12. The method of claim 1, whereinthe SA transmitted to the second device further includes a SAconfirmation flag field to indicate whether a further SA transmission ispresent after the SA transmission.
 13. The method of claim 1, whereinthe specific device includes a cluster header (CH) device orrepresentative device in a D2D device group or a device at a coverageborder.
 14. A first device for performing device-to-device (D2D)communication in a wireless communication system, the first devicecomprising: a radio frequency (RF) unit configured to receive or send anRF signal; and a processor functionally coupled to the RF unit, whereinthe processor is configured to: acquire a resource pool for the D2Dcommunication, wherein the resource pool includes a schedulingassignment (SA) resource pool indicating a resource region for SAtransmission and a data resource pool indicating a resource region forD2D data transmission; perform D2D synchronization with a base stationor a specific device; transmit an SA to a second device using the SAresource pool, wherein the SA includes information related to D2D datatransmission; and transmit D2D data to the second device, wherein the SAresource pool includes at least one of a first SA resource pool or asecond SA resource pool, wherein in the first SA resource pool, a SAresource is determined in a non-contention manner, and, in the second SAresource pool, a SA resource is determined in a contention manner,wherein the second SA resource pool includes one or more contentionwindows (CWs), and wherein, in the second SA resource pool, multiple SAsare transmitted to the second device.